An adhesive is a material that can join mechanically or chemically two surfaces. Depending on what needs to be assembled, different types of adhesives will be used. Adhesives are classified in different ways depending on their origin or their physical and chemical properties. Flooring adhesives are very numerous, complex and manufactured synthetically. Flooring adhesive must not only offer increased mechanical performance to maintain the floor bonded to the substrate, but it must also allow the expansion and withdraw of wood under varying environmental conditions of humidity and temperature.
Often called urethanes, polyurethanes are a family of products used in many areas including thermal insulation, anti-abrasion, furniture (cushions and other foams), textiles, paints and finishes, and even in the automotive industry. The great versatility of polyurethanes lies in their manufacture. Depending on the final composition of the monomer chain, it will be possible to play easily with the properties of the polyurethane and thus the final product.
Urethane adhesives are very often used in the construction industry (and therefore in the flooring industry) for their increased mechanical properties and their excellent resistance to moisture. It is interesting to know that urethane adhesives do not "dry out". Just as commonly used cements require water to reach maturity (hydration), urethane adhesives require hydroxyl (OH) groups present in the water to allow them to solidify. This property allows the installation of different coatings in the presence of moisture. If a wood floor is installed on a concrete slab, the moisture in the concrete will serve to solidify the polyurethane adhesive. That said, the conditions recommended by manufacturers of wood flooring and adhesives must always be respected before installation.
Often referred to as acrylic or acrylic-based, polyacrylics are very often used in adhesives. These acrylic-based adhesives are non-water reactive and are often water based formulated and are less expensive than polyurethane adhesives. Since their mechanical properties are often lower than those of urethane adhesives, acrylic adhesives are used when the flooring is more dimensionally stable (expansion and withdraw). They are used primarily for bonding vinyls, carpets and relatively thin engineered wood flooring. An interesting advantage of acrylic adhesives is that they are much easier to clean once finished work than a urethane adhesive.
Before applying an adhesive, all surfaces (substrates) must be structurally sound, dry, solid and stable. The substrates must also be clean, free of dust and dirt, and free of oil, grease and paint. Make sure there are no residues of curing agent, concrete sealant or old adhesive. These substances must be removed mechanically, such as scarification for example.
Acclimatizing products to their environment is also good practice. For example, the flooring will take or lose expansion and then stabilize after a few days. It is preferable that this reaction occurs before installation and thus avoid too much movement of the floor afterwards. In addition, the ambient temperature and relative humidity should always follow the recommendations of the flooring manufacturers. All these small details will ensure a good adhesion to the adhesive.
Adhesives have little influence on the acoustic performance of an assembly. However, there is sometimes a difference in performance of up to 3 points between a glued installation and a floating installation on the same structure. In addition, one of the principles to consider in acoustics to obtain a good performance is the separation of materials by resilient products. Thus, the use of a resilient acoustic membrane between the glued down floor covering and the structure allows for a greater amount of sound vibration to be absorbed.