New design trends and the increasing need to be eco-friendly, together with constant innovation in ways of preparing under-surfaces and in assembly systems for wood flooring have gone hand-in-hand with high-tech innovation in adhesive systems. It is now possible to team bonding systems specifically designed for each type of under-surface and flooring, to guarantee maximum hold over time. Adhesives are used to bond flooring to the screed or other surfaces on which the flooring is to be laid and also to stick together the tongue and groove joints on the pieces of parquet used in floating systems. The best adhesive to use depends on the type of under-surface on which the flooring is to be laid and the technical properties of the wooden flooring, taking into account the type of timber and the format. The physical and elasto-mechanical properties of the wood are different for each type of timber, type of cut or size. It is particularly important for solid wood to have a moisture content when laid almost identical to the content when it is in use. Taking all these aspects into account makes it possible to choose an adhesive with the right strength and elasticity for the flooring’s conditions of use.
There are a number of different types of adhesive:
- Adhesives in an aqueous dispersion: These are single-component synthetic resin dispersions (polyvinyl acetate). They all have a high water content and therefore they can only be used on cement screeds with a water content below 1.5%. Using them together with a primer is not recommended and therefore they have become increasingly less used over the years. They are only recommended for small wood strips laid on a traditional under-surface. Amonn offers Stufex P 90, Stufex P 90 E and Stufex 2000 HFLEX. An exception is adhesives for gluing together tongue-and-groove joints, most of which are aqueous dispersions. Amonn offers Stufex E 83 P.
- Single-component polyurethane adhesives: These are dispersions of polyurethane resins and reactive chemical groups (isocyanates). These products harden when in contact with water, both environmental and when present in the material to be bonded and they can therefore be used when the residual moisture content is above normal, up to 3%. They are highly elastic and can also be used for flooring with heating. The negative aspects of these products are their cost and the fact that they harden in contact with air, indeed, once opened, the whole of the jar must be used up.
- Dual-component polyurethane adhesives: Their technical properties are similar to single-component adhesives, but these products only dry out once a poly-isocyanate-based hardener has been added and therefore they can also be used when the residual moisture content is above normal, up to 3%, and they are compatible with insulating primers. The high degree of elasticity typical of all polyurethane adhesives makes them particularly recommended for large floor areas and those with under-floor heating. Because they do not contain amine, they can also be used by people with an allergy to epoxy adhesives and their softness makes them easy to apply. As well as wood, they can be used to bond other materials, such as linoleum, rubber, cork, carpet, etc. Amonn offers Stufex PL 97.
- Dual component epoxy-polyurethane adhesives: These are made by mixing epoxy and polyurethane resins and therefore they combine the properties of the two types of resin. As well as being economical, they are noted for their excellent adhesion but they are not very elastic and not all the formulas are recommended for large strips of flooring or flooring with heating. They can be used when the residual moisture content is normal, up to 2%, and they are compatible with insulating primers. Because the catalysers of these products contain amine, they can give rise, in susceptible people, to long-lasting allergic reactions. People with such allergies are unable to use these products and must look for a different kind of adhesive. Amonn offers Stufex PL 96, Stufex PL 200 and Stufex PL 300.
- Silane-based adhesives: These are also known as single-component reactive adhesives because they harden when in contact with the moisture in the air and in the surface. Their chemical and physical properties enable them to be used when the residual moisture content is above normal, up to 3%. They are less expensive than single-component polyurethane adhesives, although they also need to be completely used up once the jar has been opened. Amonn offers Stufex S 100.