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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.
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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.
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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.
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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.
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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.
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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. |
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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. |
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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. |
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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. |
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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. |
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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
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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.
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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
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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.
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