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Adhesives for Building and Construction - A Comprehensive Guide

Adhesives used in building and construction are versatile! Traditional and newly developed construction materials like concrete, plastics, wood panels, etc. need adhesives to display good adhesion, improved performance and easier application. Due to these benefits, the use of adhesives is increasing in the construction industry.

Learn the fundamentals of different types of adhesives, their bonding techniques and methods of application used in building and construction industry. Review:


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Construction Adhesives and Bonding


TAGS:  Acrylic Adhesives      Epoxy Adhesives      Polyurethane Adhesives    

Construction AdhesivesConstruction and civil engineering are the largest markets for adhesives as they bond large surfaces and thick joints.

Earlier bonding and sealing of traditional construction materials was done with cement, plaster and natural adhesives for ceramic tiles, erection of walls and decoration. Now, many new construction materials have been developed, such as:

  • Plastics
  • Plasterboard panels
  • Insulation foams
  • Wood-based panels (particle board), and
  • Many new synthetic raw materials for decoration

All construction materials (concrete, glass, plastics, etc.) need new adhesives in order to display a good adhesion, improved performances and easier application techniques.


The two types of adhesives used in construction are:

  • Non-structural adhesives are used to bond decorative materials, such as floor and wall coverings, and other materials which do not need very high strength (panels, fibers and particle boards, trim, some interior doors). These adhesives may be emulsion or dispersion adhesives, neoprene contact adhesives, solvent-based adhesives, natural and renewable adhesives and glues.

  • Structural adhesives give at least 5 to 8 MPa tensile shear strength. They are required for structural parts, such as bonding of concrete to concrete, ceramic tiles to concrete, masonry, construction panels, outside doors, sealing metal parts into concrete, civil engineering, composite bonding (FRP panels), metal bonding, structural glass. These adhesives may be epoxy adhesives, structural PU, silicones and structural acrylics.

All construction adhesives used on site should cure or dry at ambient temperatures i.e. 12 to 35°C according to seasons and countries, because there are no heating devices on sites. But the adhesives used to manufacture prefabricated parts in plants often use heating in order to speed up drying and/or curing.

Let’s discuss the different chemical types of construction adhesives, their formulation, characteristics, performance and applications in detail.


Chemistries of Non-Structural Adhesives


#1 Neoprene Contact Adhesives


These adhesives are based on neoprene or polychloroprene rubber, mostly in solvent solutions but also sometimes in emulsions formulated with the addition of tackifying resins and additives.
Structure of Neoprene
Structure of Neoprene

Neoprene is the trade name of polychloroprene rubber manufactured by DuPont. The main features of neoprene rubber are:

  • It should be applied always on both surfaces to be bonded and after drying the solvents of solution or the water of emulsion.
  • It leaves two films which will fuse together by a simple short contact (a few seconds) under 5 bars pressure, hence they are named contact adhesives. This will immediately give a strong bond (a few MPa) and this strength will double or triple within the next 12 to 24 hours.
  • It is very convenient for hand jobs on-site because there is no need for clamps during the drying of adhesives, and also for fast production lines.

For example: The manufacture of prefabricated panels, doors, etc. on fast lines because, after a short drying (1 minute) in force hot air oven at 60 to 90°C, parts may be assembled and given strong enough bonds for further processing, finishing or even shipping sometimes.

These are the reasons why polychloroprene/neoprene contact adhesives have been so successful since their discovery by DuPont.

Many neoprene rubber suppliers developed neoprene emulsions in order to eliminate the danger of solvents, but these emulsions have the following disadvantages:

  • They lack high tack and fast grab of solvent-based adhesives.
  • They need 30 minutes waiting and pre-drying time in order to start to develop some tack.
  • They do not wet substrates and stick as well as the solvent-based adhesives on impervious surfaces, such as metal, glass, plastics and elastomers.


Formulation of Polychoroprene or Neoprene Solvent-based Adhesives


A classical formulation comprises:

Constituents Features
10-15% Neoprene rubber Neoprene® AC soft, Neoprene® AF, Neoprene® AG
  • Fast crystallization
  • Provide very fast grab by contact
  • Shorter open time (from 30 - 60 minutes)
  • Develop quick high strength bond (within hours)
Neoprene® AD
  • Fast crystallization
  • Similar performance to Neoprene AC
  • Superior color stability 
  •  Stability of viscosity on aging at 70°C 
  •  Packaged in metal containers without discoloration
Neoprene® W
  • Excellent tack retention
  • Slow crystallization
Neoprene® WHV
  • Similar to Neoprene W but has a high plasticity value
  • Slow crystallization
  • High viscosities
  • Provide High cohesive strength
  • Used in blends with other neoprene grades in order to adjust the viscosity
Magnesium oxide and zinc oxide
  • Added to the neoprene rubber
  • 4 to 5 % of the weight of this rubber 
    • As acid acceptors - In order to prevent deterioration of the materials in contact with the neoprene rubber
    • As vulcanizing agents - It will give a slow curing of the dry adhesive at room temperature
Antioxidants
  • Prevents discoloration and aging
Resins and tackifiers   
(4 to 8% of the total adhesive weight)
  • Various resins are added to neoprene cements to obtain:
    • Longer tack retention
    • Longer open time
    • Adhesion to some materials such as metals, rubbers, plastics and other polymers
    • Higher cohesive strength and tensile shear strength
  • Some thermoplastic resins, such as derivatives of rosin, rosin esters impart tack and improve adhesion and increases open time
  • Some heat reactive resins, such as phenolics, terpene-phenolic increase the adhesion to metals, glass, plastics, and the cohesive strength of the bond.
  • Some phenolic resins can be pre-reacted with the magnesium oxide to give high melting points and high resistance to heat, sometimes up to 120 °C for some neoprene adhesives.
Solvents All solid raw materials are dissolved in an appropriate solvent blend, generally based on a mix of:
  • Ethyl acetate
  • Light ketones, such as MEK or acetone
  • Aliphatic solvents, such as hexane or cyclohexane
  • A small quantity of toluene which is a very good solvent for neoprene rubber but is toxic so limit its percentage to 5 % of total weight of adhesive
  • Dry solids range from:
    • 18% for the very fluid formulation - 100 to 300 mPa.s - which are applied by spray gun
    • up to 26% for thick formulations - 2000 to 6000 mPa.s - for trowel application
    • Higher (60 to 70%) for neoprene mastics which contain mineral fillers are applied from cartridge and piston gun.

Method of Application

Bonding Decorative Materials Neoprene contact adhesives are always applied by double application, i.e. on both surfaces to be bonded, 130 to 160 g/m2 on each side, according on flatness of surfaces. Polychloroprene/Neoprene adhesives do not fill gaps but the polychloroprene mastics may fill gaps up to 1 or 2 mm thicknesses. In construction jobs, application may be done on-site by:

  • Hand tools, such as brush & trowel
  • Spray guns or rollers for prefabricated parts neoprene adhesives

Then the solvents are left for 10 minutes to evaporate. The adhesive is dry to the touch and becomes tacky to the finger, and when the two coated surfaces are assembled the two films of adhesive fuse together immediately by simple contact under a pressure of 5 bars, such as nip rolls.

Parts must be aligned carefully because a strong bond is formed immediately by assembly and if one tries to separate it the adhesive films would be broken and the whole operation should be made again. The open time varies from 30 minutes to 2 hours according to the formulation.

Speed of setting: Immediately after assembly and pressing the shear strength reaches already 1 MPa, approximately and after 12 hours it will reach 2 to 3 MPa i.e. 80% of the final strength.

The advantages and disadvantages of Neoprene Adhesives are discussed below.

Advantages Disadvantages
  • Easy application by hand on site.
  • Very good adhesion to many materials even the impervious ones, such as:
    • Metals
    • Glass
    • Plastics (PVC, high pressure laminates, rubbers, insulation foams, etc.)
    • Concrete and fibrous materials, such as wood & particle boards.
  • Flexible bonds based on rubber, the peel strength reaches 100 to 200 N/cm
  • Good resistance from -50°C up to 130°C according to formulations
  • Good aging resistance: 20 years for inside uses but only a few years for outside uses, because the neoprene adhesives will not resist to water if the film and joint are soaked with water or humidity.
  • Flammable solvents
  • Some solvents may be dangerous for the health (e.g. toluene)

Uses of Neoprene Contact Adhesives

Neoprene contact adhesives are used to bond materials for several applications in construction, such as:

  • Decorative materials, like wood panels, PVC tiles, concrete, wood, metals.
  • Rubber sheets & gaskets.
  • Sandwich panels made of wood, plastic or steel facings, wood frames and foam insulation boards.
  • Impervious materials, such as metals, plastics& high-pressure laminates.

The are also used in footwear manufacture, furniture, construction and decoration industry.


Prices vary from 1.5 to 2.5 euros per liter according to formulations, dry solids, performances and countries (prices in Asia are lower than in western countries).


» View All Commercially Available Neoprene Grades by DuPont!


#2 Acrylic Dispersion Adhesives


These adhesives are water-based adhesives based on acrylic ester (polyacrylates) polymerized in emulsion form. They are supplied by BASF and other suppliers. They are widely used in construction to bond decorative floor coverings and ceramic tiles adhesives.


Formulation of Acrylic Floor Covering Adhesives

Polyacrylates are internally plasticized and have low glass transition temperatures, hence they are soft and tacky at room temperature. Polyacrylates show a very good resistance to plasticizers and for this reason have been the best choice for bonding of PVC floor tiles.

Later their ease of application, excellent aging and performances also allowed it to develop into wall-to-wall carpets bonding, wall coverings and ceramic wall tiles. The Acronal® dispersions which may be used for both plastic and textile floor coverings are listed below. Acronal® V 312 is the largest used acrylic adhesive.

Properties/Grades Acronal® V 312 Acronal® A 378 Acronal® A 200 Acronal® A 380 Acronal® A 280
pH 4.5 - 6.0 5.7 - 6.7 6.5 - 8.0 5.5 - 6.5 3.5 - 6.0
Solids content, % 55 62 70 62 69
Viscosity, mPa.s 30 - 150 100 - 250 150 - 500 50 - 350 200 - 1000
Glass transition temperature, °C -21 -22 -43 -22 -43
Uses Universal producer with broad range of adhesion for low-solvent and solvent-free adhesives. For low emission adhesives having a broad range of uses. For weak odor adhesives free of resins; very low emissions as per EC 1 requirements Used in formulations with soft resin; very low emissions as per EC 1 requirements. For the production of surface tackifier for carpeting, in particular with felt backing; very low emissions as per EC 1 requirements.
List of Acronal® Dispersions for Floorcovering Adhesives (Source: BASF)


A typical formulation for floor covering adhesives comprises of the following constituents:

Constituents Content
Acrylic Emulsion From 25 to 35 % by weight in wet form
Tackifying resin, such as rosin, rosin esters or others ~10%*
Fillers such as calcium carbonate or others Acrylic emulsions accept high filler ratio up to 50 to 100 % based on emulsion weight
Emulsion stabilizer
*If it is a solid form it should be dissolved first in a solvent and then mixed under high speed agitation with the emulsion, but some tackyfying resins exist also as dispersion which may be readily mixed with the acrylic emulsion.

Method of Application

All acrylic emulsion adhesives are used by one-way application i.e. on one substrate, which is generally the solid one (concrete or plaster wall). At least one of the substrates must be able to absorb the water of the adhesive in order to dry the adhesive film, but before assembly of the floor covering the worker should let the adhesive film pre-dry for 10 to 25 minutes at ambient temperature (preferably 15 to 30°C) so that the adhesive develops a high tack and will grab the floor covering immediately when assembling.

Acrylic floor covering adhesives are applied with a notched trowel. The depth of teeth controls the amount of adhesive applied, which should vary from 200 to 350 g/m2 according to roughness and flatness of materials.

After pre-drying, the floor covering is laid on the adhesive and pressed with a suitable hand tool, and the adhesive will finish drying at room temperature after a few hours through the absorption of its water by the substrates or materials. The bond will reach 100% of its final strength after 24 hours.


Performance

When these acrylic adhesives are used to bond plasticized PVC floor coverings:

  • The peel strength will reach 10 to 20 daN for 5 cm width
  • Bonds will resist to 10 or 20 years aging, and
  • Frequent cleaning of the floor with water or some humidity in the ground. 

Some acrylic emulsion grades have a good resistance to water and humidity.


Formulation Acrylic Emulsion Adhesives for Ceramic Tiles Bonding

The table below lists the Acronal® acrylic adhesives which may be used for the formulation of wall ceramic tiles adhesives. Acronal® 290 D which is the standard quality and the largest used adhesive.

Acronal® S 533 which displays a very low minimum film forming temperature (MFFT) of -1°C which allows to use this emulsion on-sites at low temperatures, while the Acronal® 290 D needs the addition of a film forming agent or plasticizer in order to allow using it in European climates.


Properties/Grades
Acronal® 290 D
Acronal® S 533
Acronal® S 710
Acronal® DS 3534
MFFT, °C
22
1
24
5
Solids content, %
50
51
50
50
Standard adhesives
X
X
X
X
Water-resistant adhesives
X
X
Formulations without film forming agents
X
X
Description
Standard
Alternative for low-emission standard adhesives
Water-resistant
Alternative for less-emission water resistant adhesives
Formulations without film forming agents
  • Ready-to-use standard quality
  • High binding capacity for fillers and pigments
  • Broad range of applications
  • High binding capacity for fillers and pigments
  • High cohesion with low MFFT even when stored at 70°C (in accordance with EN 1324)
  • High stability of finished adhesive
  • Ready-to-use adhesive
  • Water-resistant (in accordance with EN 1324)
  • Use in fields going beyond standard applications
  • Water-resistant (in accordance with EN 1324)
  • High cohesion with low MFFT even when stored at 70°C (in accordance with EN 1324)
  • Use in fields going beyond standard applications
List of Acronal® Acrylic Dispersions for Ready-to-use tile Adhesives (Source: BASF)


A typical formulation for ceramic tile includes the following constituents:

Constituents Content
Acrylic base emulsion 20 to 30 parts
Solvents 1 to 2 % to speed-up drying
Mineral Filler They must fill the gap between a construction surface
and the back of the tiles which are never flat
(castellated or embattled for the purpose of manufacturing the tiles)
Plasticizers + Additives

Method of Application

Here the tile adhesive will be applied on the concrete, plaster or panel substrate with a flat trowel first in order to deposit a thick coat (1 to 2 mm) which will flatten the wall surface. Then, it will be notched with a notched trowel with large teeth.

  • The worker will let the adhesive thicken a little bit for a few minutes, and then apply & press the tiles in the adhesive bed.
  • The ridges or fillets of adhesive will be squeezed by hand pressure and transfer to the back of the tiles (the transfer should be at least 80% of the surface)

The adhesive coat will slowly dry through absorption of the water by both substrates and through the joints, within 12 to 24 hours, according to the formulation, drying speed, and the bond strength will reach 90 % of its final strength after 24 hours approximately. The joints may be filled with a powder based jointing compound or grout after 6 hours.

Performance

  • Good resistance to water which permits the use in wet rooms, such as kitchens, bathrooms and even shower rooms.
  • Very good mechanical resistance up to 2 or 3 MPa of tensile or shear strength.
  • Very good resistance to aging up to 20 years in wet rooms.

Drawbacks

  • These adhesives which contain as much as 30 % water may fill gaps only up to 1 to 2 mm thickness because they will shrink when drying. Therefore, they are only used on walls and not on concrete floors because they are usually not flat. They require mortars (cement-based mortars) very often that can harden a thickness up to 5 or even 8 mm.
  • Acrylic emulsion adhesives are more expensive than cement-based mortars (0.4 Euros per kg) for large users versus only (0.15 to 0.2 Euros) for cement-based mortars.

Uses of Acrylic Adhesives

Acrylic adhesives in thick form as a mastic or putty are also used for bonding ceiling tiles, insulation boards, panels.

Note: Acrylic emulsions are also used to formulate pressure sensitive adhesives (PSA) in construction.

Acrylic PSA's


» Check Out Commercially Available Acrylic Polymers Suitable for Adhesives!


#3 VAE Emulsions (Vinyl Acetate-Ethylene Copolymers)


These emulsions are also internally plasticized like the acrylic emulsions and find the same applications. In some countries they are used in formulations for floor coverings and ceramic tiles bonding. Some common suppliers of VAE emulsions are Wacker, Dow, Nouryon, etc.

These are based on homo or copolymers of vinyl acetate in a water emulsion or dispersion.

  • Base emulsions have generally dry solids from 55 to 60 %.
  • They are white liquids with low viscosities (400 to 5000 MPa.s) and pH from 4 to 5.

When the emulsion is spread on a substrate, it will start to lose its water and the particles of the dispersed polymer will come in contact and will fuse together if the temperature is higher than the film forming temperature (10 to 30 °C), depending on the particle size and protective colloid. Therefore, it is often necessary to add a coalescing agent.

In order to get a ready-to-use adhesive, these emulsions should be formulated by:

  • Adding a plasticizer, such as phthalates (keeping their toxicity legislations in mind) at a ratio of a few percent based on total weight of adhesive.
  • A small amount of solvent (1 to 3%) to speed up drying and/or to facilitate the film forming and coalescence at low temperatures (10 to 15°C) which may occur in some construction sites in some countries, although such low temperatures of application are not recommended in Europe or USA, where the work on site should wait till the ambient temperature reaches at least 15°C.

In construction adhesives, these PVAc emulsion adhesives would contain mineral fillers, in order to lower cost, improve the gap filling properties, increases the viscosity in order to get a nice creamy consistence which may be applied with a notched trowel without sagging. Theses fillers are usually calcium carbonate, clay, etc.

When a high degree of water and heat resistance is needed, PVAc emulsions may be compounded with water-soluble thermosetting resins, or a copolymer emulsion having some reactive sites on the molecules may be used and crosslinked by addition of a suitable crosslinking agent or hardener. These are the ways to manufacture the E3 and E4 water resistant vinyl adhesives for wood and construction (according to European standard EN 204).

Method of Application

VAE Emulsions for Wood PVAc adhesives are applied on one of the materials to be bonded, then the worker should wait from 3 to 15 minutes at ambient temperature to let some water escape from the film, then assemble the parts, and press it for a few minutes so that enough tack is developed to maintain the parts together.

On construction sites, pressing systems are not available and therefore the PVAc adhesives which are used should have a high viscosity from 5000 to 30000 mPa.s, so that parts will be maintained together by some suction. For instance, a parquet PVAc adhesive will have:

  • Viscosity of 20000 mPa.s
  • Dry solids of 60%
  • Specific gravity of 1.27 because it contains fillers
  • Waiting time of 15 to 20 minutes at 20 °C
  • Open time of 25 minutes at 20°C.

Performance

PVAc adhesives provide fairly high mechanical resistance (e.g. for wood to wood bonds the tensile shear resistance reaches 5 MPa).

  • They bond to all porous materials, such as wood, concrete, plasterboard and plaster, textiles, cardboard, etc.
  • They do not bond usually to impervious materials, such as metals, glass, plastics or rubber (except some specially modified formulations which may bond, for instance wood to metals).
  • They are classified as E2 water resistant according to European standard EN 204, but some 1K formulation may be E3 and some 2K formulations are classified as E4.

Uses of VAE Emulsions

  • Bonding of wood to wood, wood to concrete, such as bonding wood parquets to concrete floor
  • Joining of prefabricated laminated parquets planks
  • Prefabrication of insulating panels, such as bonding of foams to plasterboard
  • Prefabrication of doors, wood windows with water and heat-resistant PVAc adhesives
  • Bonding some wall coverings (e.g. textile or paper backing)
  • Primer and tie coat when applying new concrete to old concrete
  • Vinyl copolymers may also be prepared as dry powders which are used in cement-based mortars in order to improve adhesion.

VAE Emulsions - Current Status and Future Innovations


» Explore All Vinyl Acetate-Ethylene Copolymers (VAE) Emulsions Commercially Available!


#4 Rosin Solvent-based Adhesives


Natural wood rosin or gum rosin is a cheap and renewable raw material for adhesives and glues. It is very tacky in solution of organic solvents. It is also a hard and brittle resin which cannot be used as it is, but it may be plasticized by addition of some soft polymers, such as rubbers (polyisobutylene), acrylic copolymers, etc.

Such a formulation will include:

Constituents Percentage (%)
Rosin such as WW grade 20 to 25
Soft polymer 15 to 20
Mineral Filler 15 to 20
Antioxidants, Stabilizers and Solvent blends
The balance being a suitable solvent blend depending on the solubility of the soft polymer, the rosin being soluble in many solvents namely ethyl or methyl alcohol, so that these adhesives are called sometimes rosin-alcohol adhesives. The resulting adhesives are sold at fairly cheap prices 0.8 euro/kg in Europe, even cheaper in Asia.

Method of Application

The adhesive on the concrete floor or the floor leveling compound is applied:

  • At a rate of 350 to 450 g/m2 depending on the roughness of the carpet backing
  • 5 minutes waiting time at 20°C as the solvents evaporates quickly

The carpet is laid onto the adhesive coat, pressed by manual tools, such as wood rounded tool. A complete drying of this adhesive takes 6 hours at 20 °C.

Performance

  • Peel strength after 12 hours reaches 15 kg for a 5 cm width. 
  • Aging resistance is fair because rosin will oxidate and become harder after several years, but it is good enough to last for 10 years which is the service life of the carpets.

Uses of Rosin Solvent-based Adhesives

  • They are used mostly to bond wall-to-wall all textile carpets.
  • They may or may not have a good adhesion to foam backing and to the Action back carpets where the backing is made of polyester and polypropylene yarns.
  • By using an acrylic solvent-based polymer as a modifier the rosin adhesive will bond to these backings.

» Select the Commercially Available Gum Rosins Suitable for Solvent-based Adhesives!


#5 Cellulosic and Starch-based Powder Adhesives


These adhesives are used to bond wallpapers. The powders are dissolved in water at low solids (4% for starches) and (1.5 to 2% for cellulosics), to obtain viscosities from 3000 to 15000 mPa.s. These adhesives are applied only on the back of the wallpaper, at a rate of 200 g/m2 wet.

The water of the adhesive penetrates the paper and swell it. It will enlarge by 5 %, then the wallpaper is applied on the wall and the water will be absorbed by the porous wall. The wallpaper will shrink back during drying of the water so that the air bubbles or wrinkles which may have been formed during application will also shrink and the wallpaper will be perfectly flat after drying.

The large amount of water in the glue must dry for setting of the adhesive so the substrates must quickly absorb this water. These adhesives can be used only on plaster, concrete or wall putties and renderings or wood-based panels. These adhesives can bond only to paper and fibrous materials.


Chemistries of Structural Adhesives


#1 Epoxy Adhesives


Construction and civil engineering may only use on-site adhesives which cure at ambient temperatures from 5 to 40°C. Temperatures below 5°C would not allow a proper cure or drying. Thus, the 2K epoxy adhesives are employed in the construction industry.

Formulation of 2K Epoxy Adhesives

2K Epoxy adhesives are made of two components, Part A and Part B. The Part A also called the resin, is generally a diglycidylether of bisphenol A. These epoxy resins are difunctional with epoxide groups at both ends of the molecule, and the epoxide equivalent weight is the half of the molecular weight.

Epoxy Resin
Structure of Epoxy Resin

The epoxy groups may react with polyamines, polyamides, anhydrides, and polysulfides. This reaction will give a fully crosslinked product as illustrated below.

Crosslinking Epoxy with Polyamines
Crosslinking of Epoxy Resin by Polyamines (Source: Research Gate)

The grades which cure at ambient temperatures are the liquid and semi-solid epoxy resins, with epoxy equivalent weight from 170 to 500. For instance, Araldite® 6010 is a liquid epoxy resin with a viscosity of 13000 mPa.s and epoxide equivalent weight of 190.

Other epoxy adhesives may be formulated with epoxy novolac resins, but they are very brittle.

Part B, also called hardener or curing agent with different chemical types, such as:

Polyamines - Primary amines (RNH2) will react with two epoxy groups while secondary amines R-NHR' will react with only one. Tertiary amines cannot react readily with epoxy groups but may act as a catalyst to accelerate the epoxy reaction.

For the construction adhesives formulators use liquid aliphatic polyamines or their adducts which provide fast curing at ambient temperatures, excellent chemical, water and solvent resistance.

The hardened adhesives are rigid. Pot life is short, and the reaction is quite exothermic in thick joints (1 to several mm thickness) which can be detrimental (thermal decomposition)

Heat resistance may reach up to 100°C. Ratio hardener to resin may vary from 6 to 15 % according to formulation and amine types, which might be difficult to measure accurately.
Cycloaliphatic amines may cure at low temperatures and in humid weather. They give high heat resistance and toughness. They have longer pot life than previous amines and allow thicker joints. For these reasons, they are often used to prepare thick mastics or grouts in civil engineering.
Polyamides are available in a large range of molecular weights, and the hardener to resin ratio is much higher than with the amines (1:1 ratio is possible, and this ratio is also less critical). A deviation of 10 or even 20% is acceptable without degrading the performances of the cured product.
Polyamides give higher flexibility, but other properties tend to be inferior, such as water resistance, modulus and slower speed of reaction.
Polysulfides and polymercaptans may also be used as hardeners. They give non-brittle, more flexible epoxy adhesives, and polymercaptans give fast curing at room temperature (some formulations may harden after 10 minutes only).

The epoxy formulations include these constituents frequently:

  • Reactive diluents are low viscosity, low molecular weight mono or difunctional epoxies, that will reduce the viscosity of the adhesive.
  • Fillers (e.g. talc, silica...) are added to:
    • Modify viscosity and thixotropy (non-sagging mortars for wall applications)
    • Reduce the cost of the adhesive reduce the exotherm.
    Fillers allow the adhesive to fill gaps up to 1 or 2 mm thickness (epoxy mortars for civil engineering, bonding of ceramic tiles and stones) .
  • Flexibilizers, such as plasticizers & polysulfides
  • Elastomeric modifiers or Tougheners are used to increase the peel strength or toughness of epoxy adhesives. Unmodified epoxy adhesives may be very rigid and brittle so it is necessary to add tougheners.

For example, carboxyl terminated butadiene acrylonitrile (CTBN) or amine terminated butadiene acrylonitrile rubbers. CTBN is usually reacted with the epoxy in order to improve compatibility and toughness. The ratio is usually 3 to 25% parts of rubber for 100 parts of epoxy resin.
Toughened epoxies provide high peel strength, impact resistance with little loss of modulus and mechanical resistance.

Characteristics of Epoxy Adhesives and Mortars

  • Pot life depends on the hardener, formulation, temperature and the quantity mixed. It may vary from 40 minutes for an epoxy-polyamine formulation to 100 minutes for an epoxy-polyamide, when mixing 1 kg of the 2 components at 20°C.

  • Hardening time necessary to reach 50% of maximum resistance may vary from 30 minutes up to 15 hours according to formulation, hardener, and temperature.

  • Excellent adhesion to many materials, such as concrete, metals, stone, ceramic tiles, glass, plastics, thermosetting composites & wood.

  • High mechanical strength (from 15 to 35 MPa) for the tensile shear resistance, according to the materials to be bonded and the formulations.

  • Some formulations are brittle so that it may be better to use polyamide or polysulfide hardeners.

  • Peel strength are often low (1 to 8 N/mm width according to formulations), thus it may be necessary to use the toughened epoxies which are more flexible.

  • Excellent resistance to water, chemicals, and solvents (full crosslinking).

  • The figure below provides tensile stress/strain curves for different epoxy adhesives and helps to select the type of adhesive with a modulus adapted to requirements of the bond.

    Typical Tensile Stress/Strain Cruves for a range of Epoxy Adhesives used in Construction
    Typical Tensile Stress/Strain Cruves for a range of Epoxy Adhesives used in Construction

  • Good heat and cold resistance, from - 100 to +100°C for service temperature, but some formulations start to soften at 50°C (see figure below)

    Temperature Dependence of Bulk Epoxy Adhesive Shear Strength
    Temperature Dependence of Bulk Epoxy Adhesive Shear Strength

  • Excellent resistance to fatigue
    • 104 cycles at 50 % of the maximum load
    • 105 to 106 cycles at 30%, and
    • >107 at 20%

  • Besides bonding, epoxies are also used for fixing/anchoring steel bars into concrete as shown below.

    Steel fixtures
    Fixing of a steel bar in a Tunnel Made of Concrete or Rock with Epoxy Mortar

The largest suppliers for ready-to-use formulated epoxy adhesives is Huntsman Chemicals (Araldite®) which is used in aircraft construction. All the major construction adhesive manufacturers offer epoxy adhesives and mortars, such as:

  • In Europe: SIKA, Henkel and Henkel-Teroson, Bostik Findley, PCI Germany, Mapei Italy, Dyckerhoff Germany, Deitermann Germany and others.
  • In the USA: H B Fueller, Vantico, ITW, Stonhard, Master Builders, SIKA, and others.

Get comprehensive information about the fundamentals of epoxy resins used in adhesives, main types of chemical classes and selection tips to find the right product for your adhesive formulation.

Epoxy Resin Selection


#2 Polyurethanes (PU)


Polyurethanes are semi-structural that provide a tensile shear resistance of 5 to 12 MPa. The polyurethane chemistry is rich in many polymers, reactions types, and raw materials.

There are many different types of PU formulations for use in construction. The different possibilities are:

  • Solvent less formulations, one or two components – They may be rigid or flexible according to the formulations.
  • Solvent containing formulations, one or two components – They are generally flexible.
  • Solvent less formulations – They harden by reaction with the humidity in the ambient air or in the materials to be bonded.
  • PU-reactive Hot-melts – They are used in prefabricated parts (not on-site)

Characteristics of Polyurethanes


  • Adhesion - PU adhesives adhere to many substrates, such as metals, glass, wood, plastics, rubbers. They use many adhesion systems like hydrogen bonding, covalent chemical bonds or true chemical reaction with the materials to be bonded. They also stick quite well to concrete but the high alkalinity of cement is detrimental to long range adhesion.
  • Flexibility - PU adhesives are much more flexible than the epoxies and some suppliers such as SIKA and Henkel Teroson have developed theories for using PU adhesives in Construction, transportation... for semi structural bonds. They explained that the work necessary to break a bonded joint may be higher with a flexible PU (which allows a much higher strain) compared to a rigid epoxy (which displays a high shear resistance but a low strain)
  • Crosslinkability - PU adhesives which crosslink through reaction with humidity In PU adhesives and sealants, the isocyanate groups at the end of the PU polymer react with the water contained in the air or in the materials. They may harden even in thick joints up to 20 mmm thicknesses. 
  • Extrusion - The adhesive or sealant may be extruded, for instance from a cartridge with a caulking gun and it will cure after 6 to 24 hours according to formulation, humidity, joint thickness, and ambient temperature.
  • Formulation - PU may be formulated as foamable adhesives and sealants, which are sold in aerosol cans from 500 g to a few kg sizes. When the valve is opened the product is extruded and reacts quickly with the humidity in the air, materials, and foams (with the CO2 which results from the chemical reaction and with the foaming agent in the formulation). Then it hardens in a few hours to give a foam of specific gravity from 30 to 50 g/cm3. With 1 kg of product one can get as much as 20-25 liters of foamed adhesive or sealant. These PU foams are not structural because the foam cells break under low stresses, but they are used to position and bond a door frame into the masonry, with an additional metal fastener.


#3 Structural Acrylic Adhesives


Structural or modified acrylics are thermosetting adhesives that are used in thermoplastic non-structural applications. Modified acrylic adhesives are based on polymethyl methacrylate grafted to either vinyl-terminated rubbers or polyurethane. A small quantity of hardener or catalyst is added to start polymerization. The modified acrylics used in construction may be one part, 2 part, or one part with accelerator, ambient curing systems which harden in a few minutes up to a few hours at 23°C.

According to formulations, the 2 components may be mixed just before application or the hardener may be applied on one surface and the resin or monomer on the other surface. The parts are assembled immediately and pressed together for a given time which depends on formulations.

  • They have gap filling properties up to 5 mm thickness.
  • They provide high shear resistance of 15 to 35 MPa to metals, plastics, reinforced plastics or composites.
  • Some formulations are able to absorb some quantities of rolling oils on steel.
  • They display high peel strength and impact resistance, they are much less brittle than epoxies.
  • They have good water resistance and weathering properties, and therefore they are widely used now for construction of boats and outside bonds of plastics and composites. But their cold resistance is generally - 40°C.
  • Some suppliers include: ITW Plexus, Bostik Findley (M 890), Lord (Versilok®), Loctite- Henkel, Vantico, etc.

Structural Acrylic Adhesive Formulation and Use


#4 Silicones


Silicones are mostly known as sealants, but some grades may be used as adhesives, such as the silicones for structural glazing of glass windows bonded to metal frames in the construction of curtain wall facades. These silicone adhesives are supplied by DOW CORNING, General Electric, BAYER, Germany and RHODIA France.

They have high flexibility combined with high peel and fair shear resistance. They are semi-structural because their shear resistance is only 1 to 3 MPa, and they can hold large glass windows on facades for a long period of time (probably up to 40 years or even more).

For instance, DOW CORNING 2K silicone 993 offers the following properties:

  • Dry to the touch: 80 to 100 minutes at 25°C and 50% RH.
  • Excellent adhesion to various glasses, anodized aluminum and stainless steel profiles.
  • They provide the following mechanical properties after full polymerization of 7 days at 25°C and 50%, such as:
    • Tensile resistance: 0.95 MPa
    • Tear resistance: 6 kN/m
    • Elongation at break: 130 %
    • Hardness: 40 (Shore A)
    • Service temperature: from -50°C to + 150°C
    • Long term durability

In order to bear the load of heavy glass panels it is enough to design the bonds so that the bonded surface will be large enough.


#5 MS Polymers


Silyl-terminated polyether adhesives is end capped by methyl dimethoxy silane, which may cure by moisture with a catalyst. MS polymers display good adhesion to many materials, such as metals, plastics, composites, wood, ceramics and concrete.

Advantages Disadvantages
  • Their low viscosity allows easy application by guns.
  • They cure quickly.
  • They have good weathering resistance and good mechanical properties.
  • They may be used as adhesives.
  • Medium heat resistance (75°C maximum)
  • Low shear resistance
  • They are flexible materials.

Learn more about silane hybrid prepolymers to achieve a better balance of mechanical properties (strength, elongation, viscosity control…) in your adhesives.

Silyl Modified Polymers in Adhesives


#6 Cement-based Mortars


Cement-based mortars may be considered as adhesives and are structural because they provide tensile shear resistance up to 20 MPa on concrete, ceramic tiles, bricks or stones. Their formulations are based mostly on cement and sand like a cement mortar.

In order to improve ease of use, adhesion to various substrates and other performances formulators have added several types of solid additives. These additives are:

  • Cellulosic resins
    • Acts as a water retaining agent - When the mortar is mixed with water, the cellulosic resin swells and dissolves quickly in a mode similar to the wallpaper adhesives, and retains the water in the mix so that there will be enough water in the mix to react with the cement, even if the weather is hot or the substrates absorbing.
    • Acts as a viscosity adjuster - The cellulosic resin will also help to adjust the viscosity of the paste so that it will not sag on vertical surfaces and the ribs resulting from application with a notched trowel will not flatten on horizontal floor surfaces. These ribs are necessary in order to get a good control of joint thickness and a good transfer of the cement adhesive to the back of the tiles or stones.
    • Examples of these cellulosic resins is Tylose®.

  • Adhesion promoters
    • They are used to increase adhesion on concrete, ceramic tiles, glass mosaics or stones)
    • Vinyl copolymers are solid powders which dissolve quickly when the user adds water to the powder mortar. These vinyl copolymers increase the adhesion of the mortar to concrete and ceramic tiles. Examples of these vinyl powders are Wacker VINNAPAS® or styrene-acrylate powders such as BASF Acronal® that act as flexibilizers and adhesion promoters.

The proportions of these additives are small a total of 1 to 3% based on the weight of cement is enough.

Characteristics of Cement-based Mortars

  • Water to powder ratio is usually 20 to 30%.
  • May fill large gaps up to 20 mm thick.
  • After mixing, the mix may be used during several hours
  • Hardening time must be long enough to allow the worker to install several m2 with one mixed bag
  • Open time after spreading the mortar on the substrate is usually half an hour.
  • The mortar is spread with a notched trowel on the wall or floor with a coverage of 2 to 7 kg/m2 because it is necessary to fill the gap between the substrates which may be uneven and the back of the tiles which may be grooved or fluted (not flat) and the finished surfaces must be perfectly flat however after tile installation.
  • Cement-based mortars stick well to concrete, cement, stones, ceramic tiles, glass mosaics, but they do not stick to metals or plastics.
  • Their tensile resistance is quite high, usually around 10 to 20 MPa.
  • Water resistance is excellent, similar to the water resistance of cement or concrete.

Uses of Cement-based Mortars


These cement-based mortars are used mainly for:

  • Ceramic tiles and stones bonding onto concrete walls & floors, inside & outside the buildings.
  • They are used to bond cellular concrete blocks, insulation hollow bricks, prefabricated building blocks.
  • They also for repair of worn concrete.


#7 Plaster-based Putties


These are mixtures of plaster and a few percentages of powder additives which bring improved properties:

  • Cellulosic resins control the viscosity and rheology of the paste after mixing it with water.
  • An additive slows down the setting (hardening) of plaster.  
  • Parts to be bonded may be slightly adjusted during the first hour to half hour before the plaster starts to harden.
  • Powder vinyl copolymers increase the adhesion of the mortar to the various construction materials (concrete, wood, metals)

Uses of Plaster-based Putties

  • Jointing and bonding of plaster blocks & plasterboard
  • Repairs of cracks
  • Bonding of insulation panels on walls


These plaster "mortars" are applied with a trowel to the required thickness which may be from 1 to 10 mm.



#8 Adhesives Used for Prefabricated Parts


Many parts of buildings are prefabricated in a plant, for example doors and windows, panels, insulated panels or laminated arches. This is done on high speed lines and it requires:

  • Fast bonding, fast drying or curing adhesives, such as hot-melts, solvent-based adhesives or
  • Heat-cured thermosetting adhesives, such as Urea-formaldehyde (UF) or resorcinol-formaldehyde.

Hot melts are solid at ambient temperature. On heating up to 160 to 200°C they melt and can be applied on the substrates, by cooling back to ambient temperature they become quickly hard again. Their open time is very short (only 1 to 5 seconds), and the hardening time is also very short (from 4 to 10 seconds for most formulations).

Hot melts for prefabricated parts are usually based on a mix of 3 components:

  • A plastic polymer which is usually ethylene-vinyl acetate copolymer (EVA)
  • A resin which provide adhesion to specific substrates, tack and heat resistance
  • A wax that can melt quickly and is useful to control melting time, viscosity and rheology of the adhesive.

EVA hot melts are used for bonding edges to panels on edge banding machines, for profile laminating, cabinets, countertop assembly, and sometimes to bond insulation panels to plasterboard, plywood, fiber cement, etc.

The heat resistance of EVA hot melts is limited to 60-70°C because they start to soften at these temperatures. They are thermoplastic due to the polymer and wax. Their water resistance is only fair thus for these reasons they may be used only inside the buildings.

PU-reactive hot melts provide high cohesion and high heat resistance than EVA. They are used for windows assembly, and bonding parts that must withstand temperatures up to 80°C.

Formaldehyde Resins

The UF resins and adhesives cure by hot pressing at 70 to 110°C. They are widely used for the lamination of decorative veneers or foils and films (PVC, melamine paper) to plywood, particle board or MDF.

They may be applied by roller gluing machines, with a coverage of 80 to 120 g/m2, then the laminate is applied on the glue film and parts are pressed for a few minutes at temperatures ranging from 70 to 110°C.

Resorcinol-formaldehyde are 2 components adhesives that cure at 45 to 60°C. They give a hard and cohesive bond on wood, with long durability, high creep resistance, high heat resistance and for all these reasons they have been widely used to manufacture laminated beams arches for large buildings (stadium, shopping centers, markets, swimming pools, etc.)

Other types of adhesives are used for prefabricated parts, such as:

  • Neoprene solvent-based adhesives may be sprayed on automatic lines, dried with forced hot air ovens, then assembled parts are pressed through nip rolls that gives an immediate bond by contact.
  • Vinyl emulsions are dried by hot pressing, used for wood bonding, and as primers for bonding new concrete to old one.
  • Polyurethanes (solvent-based, solvent less), 2 components are used to provide a quick setting and curing.

Having learnt about the different chemistries of adhesives used in structural and non-structural applications, now let's explore the technical, physical and mechanical characteristics of these adhesives.


Technical Characteristics of Construction Adhesives


Surface Preparation


In order to get a strong and durable bond, it is always mandatory to prepare the surfaces of the substrates so that they are:


  • Clean - The adhesive should not stick to a dirty, dusty oily or polluted surface
  • Sound and strong - The adhesives should have no loose or weak particles
  • Dry - Any moisture in the substrates would not be acceptable with solvent-based or hot melt adhesives
  • Flat - The two substrates will come in intimate contact together and with the adhesive
  • Absorb the carrier (water or solvent) - To allow the adhesive to dry


Surfaces Cleaning and Chemical Preparation


  • Concrete must be cleaned in order to get rid of dust, loose particles, pollution (such as: oils, loose paints) by:
    • Washing
    • Wire brushing
    • Sand blasting
    • Followed by vacuum cleaning or at least a good washing and wiping
  • Metals and plastics must be cleaned in order to get rid of rust, dirt, pollution, oils, etc. by wire brushing and solvent wiping. For structural bonding, metals will need adequate surface preparation by chemical etching.
  • Glass should be cleaned by solvent wiping, cleaning with water + surfactant, or chemical cleaning and preparation, followed by a thorough water rinsing in order to eliminate all contaminants. For structural bonding, glass will need a chemical treatment with a special primer ( silanes ) as recommended by the adhesives and sealants suppliers. 


Flatness of Substrates


Most adhesives require a thin joint (not more than .1 or .2 mm thickness) so that substrates should be flat and should match closely:

  • Wood surfaces must be flattened and smoothed
  • Concrete floors may need a leveling compound to make it flat enough before sticking a thin floor covering (such as a plastic floor covering)
  • The surface of panels to be covered with a thin plastic film should also be perfectly flat so that no defect will be visible after bonding.

However, some adhesives (such as the epoxies) and mortars may be used in thick layers, up to 1 mm for epoxies and up to 5 mm for cement or plaster based mortars. In these cases there is no need for a leveling compound.

Also, on the other hand, some desirable roughness is required in order to provide mechanical adhesion or "keying". Roughness may be measured with SURFTEST roughness meters.


Leveling Compounds


Powder (containing cement, sand and special additives) is mixed with water immediately before spreading on the concrete floor with a special trowel, in order to get a smooth, flat, hard and clean surface having also the required absorption.

On walls it is also necessary to smooth the surface with a filling compound or a smoothing compound, when bonding a thin wall covering (wallpaper, thin wall covering) or else the surface defects would show through.


Surface Treatments - Primers


  • If the surface of substrates is too smooth and impervious, and if the adhesive is supposed to stick through mechanical adhesion, it will be necessary to sand or abrade the substrate with a coarse sand paper or an abrasion wheel, to make it rough in order to increase the adhesion. 
  • If the surface is too smooth or difficult to adhere, some adhesives or sealants will need a primer that should be applied prior to the adhesive, and will provide chemical adhesion. 
  • Also, when the substrates absorb too much the adhesive, a primer or first coat should be applied before the adhesive, in order to fill the voids. 
  • For structural bonding of metals or glass, a specific chemical surface treatment should be made before the application of the adhesive or sealant. 
  • The surface treatment and recommended primer are usually indicated by the adhesive or sealant supplier or manufacturer.


Humidity Content


Most adhesives do not withstand humidity in the substrates. But in construction and civil engineering, moisture frequently exists inside or on the surface. Therefore it may be necessary to measure the water content with a humidity tester, refrain from bonding when the humidity exceeds a given value, and let the substrates dry, according to the type of adhesive.

As a general rule, in construction and decoration bonding, concrete substrates should not contain more than 3% humidity and wood substrates should have a humidity content near to the content it will have in the finished product and in the rooms where it will be used.

Moreover, when the weather is very humid (more than 75% RH) and cool (less than 20 - 25°C), the humidity in the air may condense on the surface of the solvent based adhesives, a blush of water condensation ( matt aspect ) will be noticed, and it will prevent a good bond.


Application Temperature (On site)


  • Should not be too high (not more than 35°C): When temperature is too high drying may be too fast for some solvent based adhesives, and open time will be too short.
  • Should not be too low (not less than 5°C): It would slow down drying and it would harm some water-based adhesives (for instance, emulsion vinyl adhesives will not give a continuous polymer film if temperature is too low)


Mixing Ratio and Pot Life


These terms are used for two component adhesives and cement-based mortars. Weight of each component should be measured as indicated in the Technical data sheets, within + or -5 %. After mixing, the chemical reaction will begin and the mix should be used within a given time which is called pot life.


Mode of Application: Tools


Adhesives should be applied with the proper tools which include:

  • Notched trowel for floor and wall coverings: The amount and thickness of adhesive will depend on the size of the teeth of the trowel, and also of the materials to be bonded. (Strictly follow the indications on the TDS of the material)
  • Brush, paint roller or spray gun, according to the job and adhesives.
  • Hand gun with a cartridge for sealants and for thick, gap filling mastics.

ToolsTools
Types of Hand Spray Guns for Construction Adhesives

Tools
Tools for Application


As a general rule, the adhesives are applied on one substrate only (generally on the rigid one i.e. on the floor or on the wall, except for adhesives that are always applied on the wallpaper).

Exception: The neoprene contact adhesives are always applied on both substrates.


Physical and Mechanical Characteristics of Adhesives


Adhesion/Cohesion, Hardening/Curing and Drying


At time of application, adhesives are liquid or paste products, so that they can be spread evenly on the substrates. They must wet and adhere on these substrates, by some mechanical/physical/chemical adhesion or attraction.

After application, the adhesive must dry or become solid and hard in order to hold strongly together the two substrates. This is called cohesion.

The hardening and drying or curing may result from various physical or chemical processes:

  • Evaporation or absorption of the liquid part (water or solvent carrier) leaving a dry film. 
  • Heat (which can speed up evaporation or induce chemical curing). 
  • Chemical reactions or polymerization or condensation.

The table shows the seven different ways of drying, curing and hardening for the adhesives used in building / construction and civil engineering.

Types of Adhesives and Sealants
Modes of setting
Setting parameters
Examples
Water based adhesives, emulsions or dispersions, aqueous solutions
Evaporation of water before assembly, absorption of water by porous substrates
Joint thickness absorption of substrates, binding forces between water and polymers
Vinyl, acrylic dispersions, cellulosic, starch powders for wallpapers
Solvent based adhesives
Absorption by substrates and evaporation of solvents
Evaporation rate of the solvents, ventilation, absorption of substrates
Neoprene mastic, PVC rosin-alcohol adhesives
Two component adhesives
Chemical reaction between the two components (with heat or at RT)
Chemical reactivity of the two components, proportions, temperature and time
Epoxies, PU, thiokols, UF, RF, MF and PF
Thermosetting adhesives one or two components
Chemical reaction (polymerization or condensation) accelerated by heat or by catalyst
Chemical reactivity, proportions, time and temperature
Urea formaldehyde, resorcinol formaldehyde, melamine formaldehyde, one component epoxies
Hot melt adhesives prefabricated
Adhesive is melted, applied and will set quickly by cooling
Cooling speed, viscosity vs. temperature, joint thickness
EVA and polyamides HM used only for parts, never on site
Humidity curing adhesives
Chemical reaction between ambient humidity or moisture in the materials and the isocyanates of the adhesive or sealant
Chemical reactivity of the isocyanate moisture in the air and in the materials, temperature
Polyurethanes, silicones (one component) MS polymers
Power mortars based on cement or plaster
Hardening of cement or plaster by mixing with water
Chemical reactivity of cement or plaster temperature
Cement and plaster based mortars
Different Modes of Setting for Construction Adhesives


Viscosity


Viscosity gives an indication of the fluidity of the adhesive or sealant. It is measured in mPa.s. The lower the viscosity the more fluid is the adhesive. It is measures with a viscosimeter, such as Brookfield viscosimeter.

Several European and American standards may be used for the measurement of viscosity:

  • ASTM D 1084-88 standard test method for viscosity of adhesives.
  • ASTM D 2256 test method for apparent viscosity of adhesives having shear rate dependant flow properties.

It is adjusted by the adhesive manufacturer in order to get the right spreading i.e. the right amount with the proper tool. The user should not try to modify it (for instance, by diluting the adhesive).

For wall application on vertical surfaces, the viscosity should be higher than for floors in order to avoid sagging.

Examples:

  • A trowelable dispersion adhesive used for the bonding of floor coverings will have a viscosity of 20000 mPa.s.
  • A solvent-based adhesive, brushable for bonding of PVC pipes and fittings will require a lower viscosity (2000 to 3000 mPa.s) in order to flow in between the two parts and spread evenly.
  • A mastic or putty for gap filling , non sagging applications on vertical surfaces, or a mortar may have from 100000 to 2 millions mPa.s.

Rheology & Viscosity Made Easy



Minimum and Maximum Thickness


  • When both surfaces are flat and smooth (for most decorative materials) the adhesives thickness should be only 0.1 to 0.2 mm after pressing surfaces together.
  • But when surfaces are not flat/rough or uneven, it is necessary to fill the joint in order to get at least 90 ]% contact between the adhesive and each substrate.

For instance, for the bonding of ceramic tiles on floors or walls, it might be necessary to apply 1 to 4 mm thickness of the cement-based mortar or adhesive. Such a high thickness is only possible with cement-based mortars because it can harden in thick coats through the chemical reaction of the cement with water, and it is non-sagging on walls.

Sealants and epoxy adhesives can also cure or dry in high thickness because they also cure through a chemical reaction. Solvent-based and water-based adhesives which dry through the evaporation or absorption of the carrier cannot be used in thickness higher than 0.2 mm because they will shrink during drying, as a result of this evaporation it will consequently not fill the gap.


Coverage or Consumption


This is the amount of adhesive which is applied on the surface, in g/m2 (also expressed in ft2/gallon in USA). It depends on:

  • The flatness and absorption of substrates
  • The specific gravity of the adhesive, and
  • Tools which are used to spread the adhesive (depth of the teeth of notched trowel, fine or coarse application with a spray gun)

Less coverage will give a poor bond (not enough contact between surfaces and adhesive). More is not good either because the solvent or the water will be trapped between the two surfaces and will dry too slowly or will not dry if substrates are impervious.


Mechanical resistance


The following mechanical properties are:

  • Peel strength (for decorative flexible coverings) is measured in kg/cm in most countries (pounds per linear inch in USA).
  • Shear strength (for structural bonds and wood-to-wood assembly) is measured in MPa (lbs/in2 in USA) with a tensile tester, such as Instron, Zwick, Lloyds or other brands. For instance, epoxy structural adhesives may reach 20 to 35 MPa, neoprene contact adhesives provide only 4 to 10 MPa, and acrylic adhesives for floor coverings provide even lesser values. There are many standards to measure these mechanical properties.
  • Creep under a given load (at a given temperature) is important for hot countries and hot places in the building. For instance, on walls and terraces in hot countries, the surface temperature of panels may reach 80°C. Many classical adhesives, such as neoprene or vinyl adhesives will soften when the temperature will exceed 60 to 100°C. Several standards allow to measure creep, for instance EN 1308: creep of ceramic tiles adhesives.
  • Elongation at break is mostly measured for sealants (in %). The elastomeric sealants for building and civil engineering may reach 200 to 300%, but a safety factor is needed so that these sealants are qualified by construction standards only up to 25 to 40% allowable elongations. Some adhesives are also elastomeric and may have up to 20 or 30 % elongation at break (e.g. PU elastic adhesives from SIKA, TEROSON or BOSTIK FINDLEY).
  • Elasticity modulus for sealants and structural adhesives
  • Hardness
  • Flexibility
  • Fatigue resistance is measured by submitting (e.g. the test samples to 1 million cycles at 25% of ultimate bond strength).


Resistance to Environmental Agents


In order to test these characteristics, the mechanical resistance of the bond is measured before and after it was submitted to these agents, and the percentage loss is recorded. Some factors to be tested are:

  • Resistance to heat, cold, aging (durability)
  • Resistance to water and humidity
  • Resistance to acids, alkalis, oils, solvents, chemicals

The specific equipment may be used for these tests:

  • Weather-o-meters such as: QUV from Q Panel USA & VOTSCH Germany
  • Salt spray units such as those from ASCOTT UK.


Environmental Risk and Safety


Some adhesives and sealants contain some chemicals which may be hazardous for the health:

  • Some solvents which are flammable or toxic, or dangerous for the environment (VOC)
  • Some hazardous chemicals, such as isocyanates, chlorinated solvents and other solvents, etc.
  • Some chemicals may cause dermatitis, for instance epoxies and polyamine hardeners, cement.

All these dangers or risks are indicated clearly on the packaging and also on TDS and safety data sheets in order to warn the end users. There is many European and international regulations for storage, transportation, utilization purposes.


Quality Control, Standards and Specifications


These characteristics are measured by the adhesive manufacturer in his plant in order to check the quality of the product and the correct proportion of the raw materials:

  • Dry solids measured according to standard EN 827
  • Viscosity/Specific gravity measured according to standard EN 542 
  • Color and aspect, pH 
  • Chemical reactivity (may be measured with a gel timer LABOMAT or according to BS 2782-835 C or others)

In many countries, adhesives and bonds must meet national, trade or international specifications and standards, such as International Standards (ISO), CEN European standards, building codes (UEATC and French CSTB, DIN, BS), national standards such as French AFNOR, British standards (BS), German (DIN), American standards (ASTM) and Japanese standards, etc. Production and QC must also follow ISO standards such as ISO 9000 series.

Now, let's move our attention towards the different construction materials and adhesive chemistries used to design a strong bond along with the uses of bonding in structural and non-structural applications.


Role of Bonding in Construction


Bonding Construction Materials with Different Adhesives


Construction of buildings uses many different adhesives and raw materials. All these materials may be bonded by careful selection of the proper adhesive, sealant or binder, and it will frequently require an adequate surface preparation.

Construction Material* Type of Adhesive Features of Bonding
Concrete
  • Cement-based mortars 
  • Epoxy Adhesives
  • Structural bonding
  • Must withstand a long exposure to water, weathering, thermal cycles outside
Stones
  • Cement-based mortars 
  • Epoxy Adhesives 
  • Acrylic Emulsions
  • Structural bonding
  • When they are heavy and attached onto walls mechanical metal attachments should be combined
Glass
  • Silicones 
  • Epoxies 
  • MS Polymers 
  • Polyurethanes
  • Avoid breakage
  • High elasticity 
  • Can withstand Elongation at break (200%) and elongation in long term stressing (25-40%)
  • Adhesion to glass must be high
Wood
  • Vinyl dispersions 
  • Rubber based (neoprene) adhesives
  • Formaldehyde resins 
  • Cyanate adhesives 
  • PU
  • Structural acrylics
  • Flexible bonds in order to tolerate movements
Metals
  • Epoxies
  • Structural bonding
Plastics and composites (reinforced plastics)
  • PU
  • Acrylics
  • Solvent-based adhesives
  • Assembled with metal fasteners
* Prior to bonding with adhesives, construction materials should be cleaned thoroughly with various techniques, in order to eliminate all contaminations, such as plaster, dirt, dust, etc.


How to Form a Bond?


Waiting Time

After application of the adhesive with the carrier, it is mandatory to wait for a given time in order to let the solvent or the water to evaporate or be absorbed by the substrates. This time is called Waiting time.

  • During the waiting time, the adhesive becomes thicker, more sticky, so that it becomes ready for assembly of the two materials. It will be able to hold the two surfaces together, hence it develops a good "tack".
  • The waiting time is shorter in hot weather, longer when it is cold.
  • The required waiting time may be:
    • 2 to 10 minutes with solvent-based adhesives
    • 5 to 15 minutes with water-based adhesives
    • Only 20 seconds for a solvent-based adhesive used for PVC pipes and fittings because the adhesive must transfer and solvate the other part.


Open Time

If one waits too long before assembly, the adhesive coat becomes too dry, hence it cannot wet and stick to the other material. This maximum time is called open time. Heat, low adhesive consumption and high absorption of substrates will reduce open time.

For instance, an acrylic emulsion adhesive used for PVC floor tiles may have an open time of 50 minutes at 20°C and 320 g/m2, but it will be only 10 to 20 minutes at 250 g/m2 and 35 °C.

Therefore, it is the responsibility of the worker (the end user) to adjust his working speed to these conditions, or to select an adhesive with the proper open time.

For the mortars the open surface should also remain wet in order for the adhesive to transfer to the other materials. Therefore, an additive is included in the formulation in order to slow down the evaporation rate if necessary.

Determination of the Right Time for Assembly
Determination of the Right Time for Assembly
WT = Waiting time and OT = Open time


Tack

The power of holding together the two materials immediately after assembly is called tack. It depends on:

  • The type of adhesives (E.g. neoprene contact adhesives used as double application display a very high tack after 10 minutes drying of the two coats of adhesive, and will give a strong bond immediately after contact under 5 bars pressure during 2 seconds)
  • The waiting time when the adhesive starts to dry it become thicker and tacky.
  • The viscosity - High viscosity adhesives tend to have a higher tack, through some suction effect.

Tack may be measured by tack tester or by a practical bonding test with the materials and the adhesive will be actually used on site.

Tack - Basics & Evaluation


Setting Time, Setting Speed

The adhesive will reach its full mechanical and chemical strength only after complete drying, curing or hardening (also called setting).

This may take from several hours up to one day, according to the type of adhesive, the absorption of materials, the temperature, the humidity in the air and the thickness of the joint.

Bond Strength
Progress of Bond Strength During First Hours/Days for Different Types of Adhesives


Design of Bonds in Construction Adhesives


  • Decorative coverings, such as wall coverings, floor coverings like carpets, PVC tiles or coverings are bonded on the whole surface. Since the mechanical stresses are low, the floor coverings stay on the floors naturally. It is enough to use a regular adhesive, such as acrylic emulsions, contact neoprene adhesive or PVAc adhesives. These will provide a good enough bond which will be able to last 10 to 20 years.
  • In case of structural bonding outside, the bond strength and design must be calculated in order to:
    • Resist to high stresses (weight of the materials and parts, weight of the building and other stresses which may result from traffic, wind, etc.)
    • Resist to shear stresses and other stresses
    • Avoid peel and cleavage stresses, and 
    • Resist for a long period of time to water, weathering, sunlight, outside temperatures and temperatures cycles, alkalis contained in the cement and other chemicals if necessary.
  • Horizontal bonds will often work in compression so that the bonds are not submitted to any separation.
  • For vertical bonds, bonding may be complemented by some mechanical fasteners if the loads are very high and if there is some risk of heavy parts falling from high level.

It is also very useful to use embedding, rabbeting, grooving, in order to eliminate the cleavage stresses and enlarge the surfaces which will work in shear, because adhesives resist much better in shear (they can reach 30 or more MPa in shear, while an epoxy structural adhesive will only withstand 10 to 50 N/cm width in peel).

For instance, segmented bridges are assembled with metal cables complemented with epoxy adhesives and the segments surfaces to be bonded are grooved in order to spread the loads on a larger area and reduce cleavage stresses.

It is also very useful to design the parts so that a stop or locking system will prevent parts to move in a non-desirable way, so that the adhesive will not be submitted to peel, cleavage or pure tension. 

Preventing Peel, cleavage or Pure Tension
Preventing Peel, cleavage or Pure Tension



Bonding: Advantages and Disadvantages


Advantages Disadvantages
Bonding allows the assembly of dissimilar materials, for instance:
  • Glass or metal to concrete
  • Plastics to wood or metals
  • Insulation foams to all other substrates.
In order to get a good and strong bond, surfaces to be bonded must be clean, dry, fairly flat (unless the adhesive tolerate thick gaps ), and these requirements are frequently difficult to satisfy in construction, where the workers work outside.
Only adhesive bonding can assemble any combination of concrete, metals, wood, stones, plasterboard, foam materials, glass, ceramics, rubber, plastics and composites with a proper selection of the adhesives. Bonding requires care, cleanliness from the workers and supervisor, and a proper training, design and adequate knowledge of bonded joints from the architects, designers, craftsmen and construction companies.
Adhesive bonding is the best method for the assembly of large surfaces that allows to spread the stresses on large areas, thereby reducing stresses concentrations. Heat resistance of construction adhesives is limited to 100°C for the best epoxy adhesives, and 70-80°C for the thermoplastic adhesives, such as neoprene or vinyl adhesives which is usually enough for outside exposure.

The highest temperatures are usually found at the surface of exterior facades panels where it can reach 70 to 80°C on dark surfaces exposed to the south, in hot countries. Sometimes the adhesives will start to soften at 60 or 70°C.

Only the cement or plaster-based mortars can withstand high temperatures, up to 300 or 400 °C, because of their mineral nature.
Bonding is the only way to manufacture sandwich panels, double panel windows (glass to glass bonding), composite boards, and it is also the only method for film laminating on panels, or attaching decorative wall coverings, or waterproofing films on inclined roofs. Heat resistance of construction adhesives is limited to 100°C for the best epoxy adhesives, and 70-80°C for the thermoplastic adhesives, such as neoprene or vinyl adhesives which is usually enough for outside exposure.

Setting time and full cure or hardening may take with some adhesives up to 10 - 15 hours at room temperature when there is a chemical reaction for curing. For instance: with 2 components epoxy adhesives, and this may require some holding fixtures during curing. But one can always find a faster curing adhesive if needed by changing the hardener or the formulation.
Bonding provides flat and smooth outside surfaces through the elimination of mechanical fasteners, such as screws, rivets, nuts and bolts or nails heads. Thus, the design is greatly improved. For instance, bonded architectural glass allows to build flat and almost seamless and continuous facades. Bonding chemistry, design and calculation of bonded parts, mechanical and physical properties of adhesives are not well known from the users and are not always clearly stated by the adhesives suppliers. On the contrary mechanical attachments are easier to use, the design and calculation of attachment is well known, and follows rules which are easy to understand.
There is no weakening of bonded parts, while with riveting or nuts and bolts requires the drilling of holes that weakens the mechanical resistance around the holes. Durability of bonds when submitted to weathering, water, heat, thermal cycles, may be limited with some standard adhesives to 10 to 15 years. Although epoxy adhesives have shown a 50 years durability in civil engineering works, such as bonded concrete segmented bridges.
The bonded part may even have a mechanical resistance greater than the sum of individual parts, for instance in sandwich panels where the sandwich displays a much higher resistance and rigidity than the resistance of the skins + that of the core. Figure 2 explains the advantages of sandwich panels. Parts to be bonded must be specially designed for bonding. For instance the bonds should not be submitted to peeling or cleavage effect or to pure tension on small surfaces, the sides of the joints should preferably be protected from water penetration because water will often degrade the adhesion by migrating at the interface.
The adhesive joints may be flexible and dampen the vibrations or withstand some differences of dilatation coefficients when the materials are quite different. For e.g. when bonding glass to metal or when the bond is very elastic and fills gaps, the jointing material becomes a sealant.
TThe cost of assembly may be lower than the cost of mechanical assembly if there is:
  • No drilling of holes
  • Less manpower
  • Low adhesive cost
  • Simple & cheap tools for applying the adhesives in construction
  • Adhesive application is usually by hand
Some mortars and thick layers of adhesive that do not shrink when curing may fill gaps and provide some leveling effect. For e.g. bonding of ceramic tiles or large concrete parts which are not flat, and for sealing metal parts into concrete.
The adhesive layer may protect from corrosion. For e.g:
  • With Epoxy adhesives it is a good electrical insulation,
  • Some adhesives used for conductive floor coverings in computer rooms or hospitals may conduct electricity
It may also provide waterproofing, depending on chemical types and formulations. For instance, a coat of epoxy, PU or rubber-based adhesive will provide waterproofing under a floor covering. This is useful for floor waterproofing under ceramic tiles in bathrooms.


End-Uses of Bonding in Construction


The applications of bonding in construction and civil engineering are divided into 2 parts:

  • Decoration and inside applications – last up to 15 or 20 years. These applications include several jobs made on site.
  • Structural high performances applications and prefabricated parts – last up to 50 years.


Decoration and Inside Applications


Bonding of Wall-to-wall Carpets

In Western Europe, wall-to wall-carpets are usually tufted carpets with foam or jute backing, and now more carpets namely "Action back" carpets where the backing is a grid made of polyester and polypropylene threads. In the past these carpets were bonded with solvent-based resin-alcohol glues, but now they are bonded with acrylic dispersion adhesives in Europe.

In Europe, carpets are bonded on the whole surface in order to prevent any "waving" of the carpet when heavy furniture are moved. The adhesives are applied with a notched trowel and the covering is usually 300 to 400 g/m2, according to the roughness of the back of the carpet and the specific gravity of the adhesive.

In some countries, such as USA, Great Britain and other English speaking countries, the residential carpets are not bonded on the whole surface, but are stretched and then nailed on the periphery of the room onto "griprods" which are usually wood profiles with protruding nails, that are themselves screwed or glued on the concrete or wood floors. In these countries, the floors are often made of wood, and the construction techniques are different than in Western Europe where we use mostly concrete floors, and nailing onto the woodfloors is easy, which is not possible on concrete).

In commercial buidings of USA and UK, floors are made of concrete and thus the carpets are glued directly to the floors or sometimes installed over padding (e.g. in offices for extra comfort). In case of USA the commercial carpets are bonded mostly with SBR latex and acrylic dispersion adhesives. The padding are bonded on the floor and the carpets are glued on the padding.


Bonding of PVC Floor Coverings

PVC floor coverings are used for commercial buildings, such as office buildings, shopping centers, hospitals and schools. In many cases they need to be cleaned by frequent washing with water and detergents and thus the adhesives must resist to water.

In Europe, USA and other countries, the main adhesives used for these PVC floor coverings are acrylic dispersions. They have a good resistance to water and to plasticizers migration from the PVC.

Some environmental organisms are against the use of PVC and therefore some countries have developed plastic floor covering made of Polyolefins. These floor coverings are more difficult to bond, but acrylic dispersion adhesives that are properly formulated have given good enough results.


Rubber Floor Coverings and Rubber Bonding

Rubber floors may be bonded with PU or epoxy adhesives, 2 components at ambient temperature curing. Sometimes it may be necessary to clean the back of the rubber with a chlorinating agent in order to improve the adhesion.

Other rubber parts may also be bonded for instance on metal or concrete with properly formulated polyurethane adhesives or solvent-based polychloroprene adhesives (by the contact, double application technique).


Bonding Parquets and Other Wood Floors

The main market for parquets is now the laminated boards which are "loose laid". This means that the boards are laid without attaching it to the floor.

In the past, the boards were jointed together by a tenon-mortise assembly and a filet of water-resistant dispersion adhesive (e.g. special vinyl glue or VAE glue) was used to bond together 2 adjacent boards. But now laminated parquets are cliped or interlocked together by a special design of the edges which allows this interlocking, thus preventing the use of glues to bond the boards together. Laminated boards may be constituted of a 3 layers system:

  • The top layer is made of a high quality wood which provide the nice aspect
  • The medium layer is made of cheap plywood or MDF
  • The bottom layer is made of a cheap softwood.

Laminated boards
Layers of Laminated Boards

These 3 layers are bonded together in the production plant, usually with melamine-formaldehyde resin cured at 80 to 100°C under pressure and sometimes using high frequency bonding.

In some cases, such as bonding on heating or cooling floors, the laminated parquets must be bonded on the floors (either concrete floors or wood floors), by using polyurethane, one or 2 components or MS Polymers adhesives (based on KANEKA Japan MS polymers).

Mosaic parquets and 15 mm thick parquet in small sections are still bonded on concrete or wood floors, mostly with vinyl adhesives but PU adhesives are more and more used for this application. MS polymers adhesives are also a good choice.

In USA, solvent-based SBR adhesives are the first choice for bonding parquets, and these adhesives are also used to bond wood based panels onto wood floor joists, by the technique called liquid nails which is a mix of nails and SBR mastics. But PU (one or 2 components) adhesives are more and more used for this, because they may be formulated as 100% solids products without solvents.

Mastic Applied by Hand Gun
The mastic (in cartridges) is applied by hand gun on the joints as a bead of 6-8 mm diameter.

Mastic Applied by Hand Gun
The mastic is also applied on the edges of the floor panels (particle boards, plywood or OSB) in order to bond it together and seal it against dust, water, insects.

Mastic Applied by Hand Gun 
Finally the floor is silent: it does not squeak when people walk on it.


Bonding Ceramic Tiles, Stones and Similar Coverings

There is now many different techniques and requirements for the installation of ceramic tiles on walls and floors, and similar mineral coverings such as natural stones, glass mosaic and thin wall decorative bricks. Tiles may be bonded on floors or walls, inside the buildings or outside, with or without waterproofing under the tiles in wet rooms or places (bathrooms, balconies) in order to prevent the water to pass through the joints and go down into the ceiling under the wet floor.

The adhesives and mortars may be rigid or more "flexible" when there is a risk of differential dilatation between the tiles and the substrates. The figure below shows a special case of bonding new tiles onto old ones with a 2K Polyurethane adhesive because the surface of old tiles is impervious and cement-based mortars would not stick to it. Therefore there is also many different types of mortars, additives, paste and ready-to-use adhesives.

Bonding New Tiles to Old Ceramic Tiles with a 2-component PU Adhesive
Bonding New Tiles to Old Ceramic Tiles with a 2-component PU Adhesive 

Let us only mention the different types of adhesives and mortars that every tile adhesive manufacturer should offer in its product range:

  • Normal thin bed mortars (rigid type, cement based with long open time, cheap formulation), wall type, floor type, used inside
  • Normal thin bed mortar, cement-based with long open time
  • High performances, high adhesion mortar for difficult-to-bond tiles and stones 
  • Thick bed mortars for large tiles and uneven substrates
  • Special mortar for swimming pools and very wet rooms 
  • Fast drying mortar 
  • 2K mortar with component A being a cement-based mortar and component B being a dispersion which provides improved performances, such as adhesion, flexibility
  • 2K Epoxy mortar for very high resistance to water (swimming pools, chemical plants) 
  • Water-based adhesive, normal grade, cheap version
  • Water-based adhesive with high resistance to water or longer open time 
  • Epoxy or 2K PU adhesives for bonding ceramic tiles on impervious substrates (older tiles or metal)
  • Several types of joining compounds, sealants and waterproofing products 
  • Sound deadening insulation systems, etc.

The most demanding application is the bonding of heavy tiles or stones on exterior walls & high rise buildings where the bonds must withstand the weight of the tiles, heat, rain, variations of temperatures and thus differential dilatation between tiles and the substrate, small movements of the building, etc. We can imagine that in the worst cases, it may become risky or dangerous to bond heavy tiles or stones on high rise buildings.

Standards for Ceramic Tiles


There is now some CEN standards for the installation of ceramic tiles, such as:

  • EN 12004 for the mortars and adhesives which defines many classes (C1, C1,T, C1E, C2E, C2T, C2G, D1E, D2E, D2TE, RG, etc.)
  • EN 13888 for joining compounds
  • French certification CSTbat 2001 for ceramic tiles adhesives

There are more standards to come in the next years.

In USA, there are several standards and codes of practice, such as:
  • The Handbook for ceramic tiles installation of the Tile council of America
  • ASTM C 658 and ANSI A 118.3 specifications for chemical resistant resin grouts, and others.


Bonding Wall Covering and Wallpapers Inside

This is a more simple operation. Several types of adhesives are used:

  • For wallpapers, the usual technique all over Europe is to use powder glues based either on cellulosic resins (methyl cellulose or carboxy methyl cellulose) or starch which are dissolved in water immediately prior to the utilization. The solids contents is very low (2 to 4%) according to the grades of polymers. The liquid adhesive is applied onto the back of the wallpaper which is left 10 minutes so that the water of the adhesive will swell the paper that will enlarge by some 1 to 2%, then the wallpaper is applied on the wall. After one night, the water dries and the wall paper will shrink back to its original dimensions, so that any wrinkle or bubble will disappear leaving a perfectly flat surface. But in USA, people are switching to ready-to-use dispersions based on vinyl or VAE dispersions.
  • For the vinyl or textile wall coverings, everybody in both countries uses ready-to-use vinyl, acrylic or EVA dispersions adhesives.

Bonding Wall Covering with a Vinyl Dispersion
Bonding Wall Covering with a Vinyl Dispersion

Bonding Gypsum Boards

Gypsum boards are a huge market for interior walls, for instance the American and European market reaches ~300 millions m2. In the past, gypsum boards were usually installed by screwing it onto wood studs, but now it may be bonded onto these wood studs or even directly on the concrete or concrete blocks walls.

This can be done with thick solvent-based adhesive mastics based on neoprene or SBR, which are applied from cartridges with a hand gun. Then the joining of panels together also needs a joining compound which may be either a ready mix paste (based on CMC or PVAc emulsion filled with some calcium carbonate) or a powder based on plaster modified with an additive which slows down the hardening of the plaster and some thickener to control the rheology of the mix with water.


Roofing Adhesives and Tapes

Recent roofing waterproofing systems include a vapor barrier, an insulation board such as PU foam and a polymer or rubber membrane which is bonded onto the insulation board, thus eliminating the need of a heavy ballast on the top which was usual in the past.

Mechanical fasteners or heat welding of the membrane rolls are also widely used instead of bonding. PVC and EPDM are the major membranes used in Europe and USA respectively. PVC membranes are bonded with polyurethane adhesives or nitrile adhesives, while EPDM membranes are bonded mostly with solvent-based neoprene adhesives.

Membranes may be bonded on the whole surface of the roof or only bonded at the seams. But, in order to resist to wind suction effect and to hold it on slopes or vertical surfaces, it must be bonded on the whole surface.

Butyl rubber tapes are used for the seams between 2 adjacent EPDM rolls, while the seams on PVC may be done by heat sealing or by bonding with PU or nitrile rubber adhesives.


Plastic Pipes Joint Cements

In Europe water plastic pipes are made of PVC or CPVC the latter for heat resistance, in USA it may be PVC, CPVC or ABS. The rule for adhesive selection is simple.

  • PVC pipes are bonded with adhesives based on PVC dissolved in a strong solvent, usually a mixture of tetrahydrofuranne and ketones. As tetrahydrofuranne (THF) is a strong solvent, dissolves the PVC on the surface thus providing a solvent welding.
  • CPVC pipes are bonded with adhesives based on CPVC. It is also dissolved in a mixture of THF and ketones.
  • ABS pipes are bonded with adhesives based on ABS solutions.

Thanks to the THF, there is actually a solvent welding of the polymers, but the adhesive contains also 15 to 30% of PVC in order to fill the thin gap between the male and female parts. When the bond must resist to pressurized water (supply of water in the high stores buildings), the bond must be very reliable and needs a true solvent weld, which means that the adhesive must contain THF. There is a number of standards in Europe and in USA for the plastic pipes joint cements.


Interiors Panels

These panels and partitions are prefabricated in factories but some decorative panels are bonded on the walls, usually with polychloroprene or SBR solvent based mastics, sold in cartridges.

Beads of mastic, 5 to 8 mm in diameter are applied on the back of the panels, one line every 10 or 20 cm.

  • The panels are immediately pressed onto the wall (concrete or concrete blocks for instance), so that the adhesive transfers to the wall, then the panel is detached from the wall, laid on the floor for a few minutes in order to flash off the solvent so that the adhesive becomes very tacky.
  • Then the panel is pressed again on the wall at the same place, the 2 lines of mastic 'fuse' immediately together, providing a bond immediately, which is strong enough to hold the panel.

Adhesives are used to attach interior panels made of gypsum board, lauan or plywood to wood studs and framing. This technique is frequently used in USA and also in European Nordic countries where many individual houses are made of wood. Adhesives may be used along with nails in order to secure the bond when the builder do not rely on adhesives alone for a long term durability.

Thin plastic panels (3 mm thick) such as Polystyrene, ABS or FRP are sometimes attached to drywall in bathrooms and kitchens.

High pressure laminates, such as Formica, Polyrey and other brands may be bonded on site on MDF or particle boards with polychloroprene solvent based adhesives to make kitchen panels and shelves, in some developing countries where these kitchen furniture are not prefabricated but rather made on site, to the required dimensions and styles.


Bonding Thermal and Sound Insulation Panels

These panels may be PS, PU foam, other foams, glass fiber panels and mats, and it may be bonded with acrylic or SBR emulsion adhesives inside the buildings. Some insulation panels are composite panels made of glass fiber rigid panel bonded in the factory onto a gypsum board, such as CALIBEL from Saint Gobain and others.

Then on site, the whole panel is bonded onto concrete walls with a plaster-based mortar or putty.


Bonding Thermal Insulation on the Outside of the Walls

This technique called "exterior insulation" has been used since 25 years (it started in Germany in the years 70).

Foam panels are bonded on the outside of the all, usually with a cement-based mortar. Then a polyester reinforcing grid is bonded on the foam and embedded into a decorative cement-based mortar or a decorative acrylic dispersion coating. Here the adhesive must resist to long term exposure to weathering, sun, rain & thermal cycles.

Some new systems including decorative bricks bonded onto foam insulation boards gives insulated and decorative panels which are then screwed onto the exterior wall. These systems are used in Netherlands and Belgium.


Solar Control Films

These are plastic films which are bonded on the exterior glass windows or glass panels in order to reduce the sunlight inside the rooms.

Reflective films include silver colored vacuum metallized films or tinted films. The reflective film is composed of:

  • A coating outside
  • A metallized polyester film
  • A laminating adhesive
  • Another clear polyester film with UV inhibitor
  • A pressure sensitive adhesive coat, and
  • A release liner

Usually solvent-based pressure-sensitive acrylic adhesives are used for both laminating and bonding to the glass. Solvent-based polyester adhesives are used for bonding together the 2 plastic films.


Structural Applications and Prefabricated Parts


The structural and outside parts must be properly designed for safety by the following means:

  • Whenever possible the high loads should be carried by both the structural adhesive and some mechanical help: adhesives bonds may be complemented by some mechanical fasteners if there is some risk of heavy parts falling from a high level
  • Use embedding, rabbeting and grooving in order to eliminate the cleavage and peel stresses and make sure that the bonds will work in shear rather than in cleavage, peel or tensile strength
  • Protect if possible the adhesive layer from excessive contacts with aggressive media such as water, chemicals & heat
  • Use adequate safety factors in the calculation of bonded joints and bonded surfaces.

A number of examples of bonded parts where the parts have withstood long term exposures in construction and civil engineering are discussed below.


Bonding of Concrete for Segmental Bridges

Epoxy adhesives show a high adhesion to clean concrete, better than normal cement based mortars which require a perfectly clean and sometimes fresh concrete. They may be also formulated to provide a faster hardening than cement-based mortars.

The first segmental bridges have been bonded in Europe using epoxy adhesives. Here the concrete hollow blocks or segments (10 meters long) are bonded together and pre-stressed in order to form monolithic long span bridges.

Epoxies display excellent adhesion to concrete, even freshly cast, high mechanical resistance and proven long term durability. They have replaced cement-based mortars since many years.

The adhesive does not bear all the load because:

  1. The segments have a special design where there is a keying which fits together the 2 adjacent concrete blocks so that there is a complementary mechanical fastening and joints are stressed with a mix of compression, shear and cleavage
  2. The steel cables used for pre-stressing the concrete also contribute to a large extend to the overall mechanical strength of the bridge.

But the epoxy adhesive also bear a part of the total load.

In order to provide this keying, the precast concrete segments were "counter cast" for the first time on the Choisy bridge. Each concrete segment was cast directly against the previous one where the mating surface, with the proper keyed design was coated with a release agent, so that the second segment was molded onto the first one, thus giving an almost perfect match and therefore a fairly thin joint (1 to 2 mm thickness) which could be filled with an epoxy adhesive at an inexpensive cost.

Segmented Bridges
Construction of Segmental Bridge

In these segmental bridges we may consider that the epoxy adhesive has several advantages and functions as compared to cement mortars. They are:

  • It bonds the surfaces so that compression, shear and in some cases also tensile stresses are transmitted between the segments.
  • It cures fast enough so that it allows a continuous erection of the segments.
  • It lubricates the surfaces of the joints to facilitate a proper positioning of the segments during erection
  • It provides a watertight seal of the joints so that the steel cables are protected against corrosion.

The technical characteristics of SIKA epoxy adhesive SIKADUR 31 SBA, types S-03 and S-04 specially designed for segmental bridges are:

  • Mixing ratio: 100 parts by weight of ENOCOL resin for 20 parts of hardener
  • Pot life at 20°C: 2 hours
  • Required humidity in the wood: 10 to 16 %
  • Coating weight: 300 to 600 g/m2
  • Minimum press time: 1 hour at 40°C or 20 min at 60°C for bended beams increase press time 40%
  • Pressure 7 to 14 bars
  • Meets DIN standard 68705 for AW 100 bonds and BS 1203 and 1204 for WBP bonds
  • Tensile shear testing give rupture into the wood (at least 5 to 6 MPa)


Concrete Parts in Civil Engineering

Pavement borders, steel or concrete poles, prefabricated concrete panels... are now more and more often bonded on concrete with epoxy adhesives instead of cement mortars. Epoxy adhesives are no longer considered as too expensive for these jobs because they may be heavily filled with sand, up to 500 parts of sand for 100 parts of epoxy resin, so that the selling price of the epoxy mortar is lowered down to some 2 euros/kg.


Reinforcement of concrete buildings and civil works

When concrete structures are damaged their mechanical resistance is lowered and it may become necessary to reinforce it. It is also necessary when the structures must bear higher loads than initially planned (for instance increased traffic and loads on a bridge).

Since 1970, many concrete structures have been reinforced by bonding steel plates (a few mm thick) onto the concrete, with 2 components ambient temperature curing epoxy adhesives, in order to increase mechanical resistance to deflection under loads.

This technique started in France with the procede UTI L' HERMITE. It was also used on a very large scale in the seventies in Switzerland and Japan. More than 500 bridges have been reinforced in Japan in order to bear the increase of heavy traffic since these bridges were built.

In England the reinforcement of several motorway bridges, floor beams of buildings, of car parks and many other examples, since 1975.

The figure below shows an example of a reinforcement of a concrete bridge by bonding steel plates, 3 mm thick, inside the hollow structure, which protects the bonds from corrosion and weathering , with an epoxy adhesive SIKADUR 31 from SIKA. The concrete and the steel plates were sand blasted, the steel plates were applied at a 30°C angle in order to bridge the existing cracks, and pressed against the adhesive and concrete by using props and struts.

Reinforcement of a damaged concrete bridge by bonding steel plates with epoxy adhesive
Reinforcement of a Damaged Concrete Bridge by Bonding Steel Plates with Epoxy Adhesive 

Many other similar site jobs have been realized by bonding either steel plates or, recently, carbon fibers fabrics impregnated and bonded to concrete with epoxy resins.

Several companies are offering such systems based on carbon fibers fabrics, such as MAPEI Italy, Huntsman Chemicals and others in Japan.


Bonding Wood for Laminated Beams Arches (or Glulam)

This technique was initiated in Europe by German and Nordic companies in the sixties. The idea was to manufacture very large structures, up to 40 m span, by bonding together wood lumber pieces or thick boards, 2 to 5 meter long, as shown below, formed in a straight or curved shape as required by the architects.

Laminated beams architectural glulam
Laminated Beams Architectural Glulam

The best adhesives were found to be the thermosetting, 2 components resorcinol-formaldehyde glues (RF) because:

  • They give a very strong and stiff bond which will not "flow" under high loads and stresses.
  • They have an excellent long term resistance to aging, humidity, fire, and insects.
  • They have an acceptable price of ~3 euros/kg in large quantities.

Later, when prices of large lumber pieces increased, it became obvious that this technique would allow to use shorter pieces, and even recovered pieces which were not "square" so that their price was much lower, and computer controlled sawing, cutting and lay out allowed to assemble these various length and shapes in a proper way.

The RF glues are 2 components glues which cure at 60 to 70°C under pressure for 15 to 40 min. The main characteristics of ENOCOL RLF 185 a RF glue from ATO FINDLEY France specially designed for glulam bonding:

  • Mixing ratio: 100 parts by weight of ENOCOL resin for 20 parts of hardener
  • Pot life at 20°C: 2 hours
  • Required humidity in the wood: 10 to 16 %
  • Coating weight: 300 to 600 g/m2
  • Minimum press time: 1 hour at 40°C or 20 min at 60°C for bended beams increase press time 40%
  • Pressure 7 to 14 bars
  • Meets DIN standard 68705 for AW 100 bonds and BS 1203 and 1204 for WBP bonds
  • Tensile shear testing give rupture into the wood (at least 5 to 6 MPa)


Wood Reinforcements

Damaged timber may be repaired as shown below. The reinforcing bars may be steel rods or pultruded rods made of carbon -epoxy, and these rods are bonded with epoxy resin.

Repair to Timber Section
Repair to Timber Section


Wood-based Structural Panels

Floor or exterior wall panels may be manufactured by bonding wood or wood based panels onto wood joists or wood frames with high resistance phenolic glues. These glues are cured by heat and under 10 bars pressure in the factory. RF glues may also be used and cured at 40 to 50°C. Ambiant temperature curing adhesives (UF, RF, epoxies) may be also used on site, if necessary.


High Resistance Plywood

High resistance plywood may be used for factories floors are made of birch plies bonded with phenolic resins. They resist to boiling water, outside weathering and meet the WBP requirements and the following standards: EN 314 - 2 / class 3, DIN 68705 part 3 / type BFU 100, and also to the E1 standard related to formaldehyde gas release in the ambient air.

Bonding Glass for Architectural or Structural Glazing

Bonding Glass for Architectural or Structural GlazingStructural glazing is a method utilizing a silicone adhesive to attach strongly and durably glass to the structure of a building. The wind load and the weight of the glass panels are transferred through the silicone adhesive / sealant to the structure of the building.

This is a very demanding application because the whole system depends on the adhesion and the internal cohesion of the adhesive and its durability, and there is obviously a risk if the glass panel would fall from a high level.

However some mechanical fasteners (small metal clips which are almost invisible) are added in order to provide additional safety. This technique provides a beautiful aspect because the glass facade looks as a continuous wall almost seamless.

  • These systems must be carefully designed and calculated, the technical characteristics of the adhesives must be carefully assessed through various laboratory tests.
  • The glass must be bonded to its frame only in plants, under strict control (it can never be bonded on site because bonding conditions would not be constant and reliable).
  • The bond must be flexible in order to accommodate the different coefficient of dilatation (glass versus metal frames), the wind stresses and the movements of the structure.
  • The adhesive must have a long term durability, and the silicone manufacturers usually provide a minimum 10 years warranty, besides this, the bonds must be inspected on a regular basis in order to detect any defect before it becomes dangerous.

To ensure long-term durability for structural glazing, several European and other standards must be satisfied, such as:

  • Guidelines for European technical approval for structural glazing (ETAG 0022 part 1 september 1998)
  • CEN draft European standards CEN TC 129 / WG 16 - PrEN 13022, October 1997
  • Vitrages exterieurs colles faisant l'objet d'un avis technique, conditions generales de conception, fabrication et mise en oeuvre (Cahiers du CSTB 3130, mai 1999) in France
  • BSI: BS 6262 Code of practice for glazing for Buildings, Part 6, special applications (UK)
  • Standard guides for structural sealant glazing: ASTM C 1401-98 (USA)
  • GB 16776 – 1997: Structural silicone sealant for building (China)

The silicone adhesives/sealants which are used have only 1 to 2.5 MPa tensile resistance but this is enough provided that the joint total surface x tensile resistance exceeds by far the weight of the glass and the forces arising from wind effects and movements of the building.

Silicones for Glazing
Functions of the Silicone in Architectural Glazed Glass Panels

The main technical characteristics of a typical silicone product for structural glazing, DOW CORNING 993:

  • Viscosity: 40 000 mPa.s
  • Open time: 10 to 30 min
  • Dry to the touch: 80 to 100 min.

After 7 days polymerization at 25°C and 50% RH:
  • Tensile strength: 0.95 MPa
  • Resistance to tearing: 6 kN/m
  • Elongation at break: 130%
  • Shore A hardness: 40
  • Service temperature: -50 to + 150°C


Insulated Glass (Double Glass Panels)

Figure below shows the general design of these insulated glass windows and the various adhesives and sealants which are used for the various materials, bonds and seals.

Several companies manufacture complete ranges of adhesives and sealants for the insulating double windows. For example: KOMMERLING (Germany), BOSTIK-FINDLEY (UK), TREMCO (USA and Europe), etc.
window panes
Double Glass Panels in Window Panes


Bonding Metals

Metals are seldom bonded in construction because it is more simple to assemble it with screws, bolts, rivets or welding and these techniques are well known for many years, unlike adhesive bonding. However, some applications in which light, thin, metal decorative panels or metal sheets could be bonded on various substrates or onto metal stiffeners. These applications have the following advantages:

  • No visible attachements thus providing a nice, smooth and perfectly flat surface for an improved aspect
  • No holes to be drilled and no corrosion or staining as would occur around metal fasteners
  • No deformation of the thin metal as it would occur if it was riveted or screwed or welded
  • Lighter construction: adhesive bonding allows the use of thinner metal sheets compared to welding, riveting, and the adhesive itself weighs less than bolts, screws or rivets.

Bonding Metal facing sheets
Metal Facing Sheets

Studies have been made also to replace welding of hollow bars or tubes because welding on site may be difficult. These hollow sections may be used as bridge parapets or building elements.

The problem is that for bridges construction a design life of almost 100 years is required and no synthetic adhesive has such an experience of durability so far, but epoxies may be able to withstand such a service life, if we consider the durability curves which are available. A good start could be to try epoxies for repair jobs which are expected to last only 20 to 50 years.

Starting in 1952, exterior metal pipes for gas distribution in private housing have been bonded with 2 components epoxy heat curing adhesives, in France, and are still leak proof after 30 to 50 years, under a 5 bars pressure.

Sandwich panels made of metal honeycomb bonded onto metal sheet facings in a way similar to the aircraft panels should also be used in construction for special partition or to manufacture lighter elevator cabins for instance because of the weight.


Bonding Exterior Decorative Panels

Several adhesives manufacturers have started bonding exterior decorative panels since 1995. The SIKA TACK Panel adhesive which is used for concealed mounting of ventilated façade panels such as TRESPA Meteon, Alucobond and Perstop Exterior. These panels are 4 to 7 mm thick and they weigh up to 10 kg/m2.

sika ventilator Panels
Ventilator Panels (Source: SIKA)

SIKA TACK system includes first a double faced pressure sensitive tape which is used for immediate holding of the panels until final cure of the actual adhesive, and second the SIKA TACK adhesive, a 1 component moisture curing polyurethane adhesive. The main technical characteristics of this adhesive are:

  • Tack free time: 20 min at 25°C and 50% RH
  • Curing speed: 4 mm thickness per 24 hours same conditions as above
  • Service temperatures: -40 to + 90°C
  • Tensile strength: 4 MPa according to DIN 53504
  • Tensile shear strength: 2.5 MPa

It is assumed that the bonded area is large enough in order to be able to bear the weight of the panels, with a large safety factor. This is quite an interesting new technique which is already used on a large scale, and it is quite promising for many commercial buildings which are erected nowadays in developing countries such as China.


Fixing and Anchoring Steel Rods and Bolts in Concrete

The figure below uses either chemical plugs containing the 2 components which are mixed after breaking a separation barrier between the 2 components or a 2 component cartridge which injects the mix into the hole.

Several suppliers exist on the market, such as HILTI, ETANCO (France), WURTH (Germany) and others.

This technique utilizes polyester resin, epoxy resins or recently epoxy-acrylates.

Cement-based mortars are also used in a classical way in order to anchor bolts, rods, metal fastening parts into holes in concrete.

Anchoring of Steel Rods/Bolts into Concrete with Chemical Plugs
Anchoring of Steel Rods/Bolts into Concrete with Chemical Plugs


Commercially Available Additives & Polymers for Construction Adhesives






Polymer ApplicationSealants for Construction - Know More

Polymer ApplicationStarting Point Adhesive Formulations for Construction

Innovation days 2021
For stronger adhesives stick to Nynas
2 Comments on "Adhesives for Building and Construction - A Comprehensive Guide"
Mehul J Nov 21, 2020
Superb + Comprehensive information. Many thanks!!
David W Aug 14, 2020
Can I get this as a PDF to highlight and mark up as I read? I'm still an old school paper reader. Thanks Dave

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