Contact adhesive for stairs and skirting
There are two properties that are predominantly responsible for giving the contact adhesives their outstanding performance. They are the only wet adhesives that deliver an immediate bond - an equivalent effect can otherwise only be achieved through mechanical bracing or adhesive tapes. Their range of use is also extremely broad, so they can often be used as problem solvers for difficult bonding jobs. Contact adhesive for stairs and skirting installation are common. Most products today are still solvent-based, which are often no longer suitable due to environmental and safety reason. This article examines the current state of technology and the situation with environmental concerns as well as health & safety issues.
Applications of contact adhesives
Regardless of whether it’s solvent or solvent free contact adhesive, virtually all standard building materials like screeds, levelling compounds, plasters, and installation or metal boards are suitable. The surface in question should be as smooth and flat as possible. Smooth dense substrates like metal boards, old floors, or finishes must be thoroughly sanded and vacuumed. Dust-producing surfaces such as calcium sulphate screeds, or chipboard must be primed and then a smoothing compound applied. For floor coverings that need to bee adhered around edges or corners, there will be a permanent high tensile stress effect caused by strain. Typical cases include flutes, the outer edges of skirting, or staircases. Contact adhesives can provide adequate strengths here.
The immediate bonding strength causes floor coverings, skirting, capping & coving to retain their shape despite the sometimes high tensions from the outset. The high final strength guarantees extremely long-lasting bonding. Suitable subfloor preparation is a prerequisite.
Although not necessarily typical, contact adhesives can be used to install smaller floor coverings directly adjoining a stair step, or if resilient floor coverings needs to be adhered in lifts. The requirement for extensive bonding of floor coverings can also exist for walls. These are often impact walls in sports facilities, but also floor coverings that are adhered to the wall in schools or hospitals.
Since the load must also be absorbed by the dead weight of the floor covering when wall mounting adhesive, extreme point loads can occur due to “ball impact”. The high performance capacity of contact adhesives is essential for long-lasting bonding. For a long time, impact wall installation was only achieved by solvent-based contact adhesives. Now, however, these requirements can also be met by solvent-free adhesives. A hugely welcome development due to the health & safety concerns with using harmful solvent based adhesives for large areas or in sealed rooms.
The environment and safety
Solvent-based contact adhesives are useful and are a very reliable group of adhesives. Their comparatively high solvent content of about 70-80%, however, holds two considerable risks. For one inhaling solvents is harmful to those installing the adhesive and for those which occupy the space. Secondly contact adhesive are highly flammable and have a high risk of explosion and fire.
A thoroughly realistic scenario that is unfortunately confirmed again and again by corresponding accidents. In accordance with best environmental practice, solvent-based products ultimately might no longer be used at all. The manufacturers of installation materials continue to make major efforts to reduce emissions from adhesives. The continued use of solvent-based products is counter-productive to this and is simply outdated.
Principles of contact adhesives
Contact adhesives are applied to the parts being bonded on both sides, for example for skirting, it is applied on the back of the skirting and on the wall. They then flash off until the solvents or dispersants are completely evaporated. Then the “contact bonding time” begins. This is the time in which the dried adhesive on the floor covering continues to merge upon contact with the second, also dried adhesive on the substrate. The contact bonding time depends on the product, and generally takes between 2 to 12 hours.
The double-sided application is a disadvantage in comparison to single-sided adhesives (pressure-sensitive or wet adhesives). However it there is one advantage as the floor covering can, for example, be covered and stored temporarily at almost any time. The actual bonding, then, occurs once the coated floor covering has had contact with the coated substrate.
The binding agent in most contact adhesives is usually polychloroprene, which is also marketed under the names Neopren or Neoprene (R). During bonding, the two dried adhesive areas are pressed against each other with high pressure for a short time. This causes crystallisation to occur inside the adhesive layers and high forces of adhesion combine with the immediate bonding strength described above. This process is known as filming. Afterwards, the adhesive strength continues to grow with the final strength reached after one to three days.
Often the user doesn’t know of the immediate strength, because other types of adhesive often have a perceptible initial bond. An indication of this can be seen in the form of threads forming, seen by many installers as evidence of quality. However, the tack can only hold the floor covering on the floor for a limited time if this is under tension. Bonding is not permanent with these adhesives until the adhesive strength has slowly built up during the setting phase. The final strength reached after this ensures that the floor covering is stuck despite the occurring stress. Adhesive tapes used in skirting areas behave in a similar way. As pressure sensitive adhesives, they have a high initial bond. For floor coverings with long-term tensile forces, which occur in tight radii on stair noising, they can reach their boundaries in function. Since they are completely harmless for environmental and worker health reasons, they should be used where possible as alternatives to solvent-based contact adhesives.
Performance capacity of contact adhesives
In the past, solvent-based contact adhesives were superior to the few dispersion products on the market. This dominance has been overridden with the latest generation of solvent free water-based neoprene contact adhesives. The immediate bond strength in both product types is now similar. The final strength of the solvent-free adhesives, measured as shear resistance under vinyl, is about 30% higher than that of the solvent-based adhesive. With corresponding peel resistance, the water-based adhesive surpasses its predecessor by almost double!
The high storage temperature of 50 °C show the outstanding resistance against possible impact from plasticisers in vinyl floor coverings. In practice, the installer has a high level of security, particularly with flexible skirting or floor coverings with high plasticiser content,such as cushioned vinyl or PVC floor coverings. The contact bonding time of solvent-free adhesives, at least two hours, is long enough for all standard applications. Covering the back of the floor covering the day before installation can also be done, which offers the installer additional flexibility for installing. The coverage for both types of adhesive are quite high. For solvent-free contact adhesives, however, it’s especially important, because this is the only way to achieve setting times that will be accepted by the installer. However the setting time increases when transitioning from solvent to solvent-free (water) at room temperature, from about 10-20 minutes to about 20-40 minutes. The installer’s health and that of their environment should be worth the additional 10-20 minutes. Notwithstanding the above, the installer can drastically reduce setting time without impeding features at any time by using a hot air blower.
Contact adhesives are an extremely versatile adhesive group and occupy a special position thanks to their immediate adhesive effect. They are technically well engineered and proven in practice. Dispersion-based products can now be used as a technical equivalent to solvent-based products. The argument of technical necessity therefore does not apply in future as a rationale for using out-dated solvent-based adhesives. These products which are criticised from an environmental and user perspective should thus be scaled off in favour of water-based alternatives as soon as possible. Then, this very useful group of adhesives can be recognised for their high value in the future.
Contact adhesives - comparison of select technical properties
|Property||UZIN WK 222||UZIN GN 222|
|GISCODE||D 1 (solvent-free dispersion)||S 1 (heavily solvent-based)|
|Easy to spread||very good||good|
|Open time||20 – 40 min.||10 – 20 min.|
|Consumption (PVC)||approx. 150 g (both sides)||approx. 200 g (both sides)|
|Consumption (needle felt)||approx. 500 g (both sides)||approx. 500 g (both sides)|
|Shear resistance (50 °C/6 weeks)||133%||100%|
|Peel resistance (50 °C/6 weeks)||185%||100%|