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Make Sure You Back The Right Horse

Martin Cummins on the technical needs of adhesives

LAST month I discussed why manufacturers offer ranges rather than just a single product, specifically about adhesives and the need for different handling characteristics of products depending on what was being bonded, the ‘horses for courses’ reference.
In this article I would like to expand on this theme and discuss the different technical needs of adhesives depending on the floorcovering, the service conditions and even the subfloor.
n Carpet tiles: Most flooring contractors would agree that installations of carpet tiles are the easiest to carry out, but are they aware of what goes into an adhesive to make it suitable for this application?
The material that helps to stick the tile down and allow it to release again is called a polymer. Selecting a polymer that isn’t too aggressive in tack is crucial. Otherwise you will end up with a permanent bond and not a release bond.
n Metal access: The adhesive also has to be formulated to enable it to be used on ‘difficult’ substrates such as metal access. The wrong formulation can result in corrosion of metal or interactions with the metal that result in a deadening of the adhesive tack. So control of the pH in adhesives is vital.
n Carpets: When it comes to bonding carpets the requirement is for an adhesive that has sufficient early strength (sometimes referred to as grab) to resist the ‘curl back’ of the carpet during installation. Generally the adhesives combining rubber and resin have the greatest resistance to curl and have been the industry standard for some time now.
Carpet adhesives also need to have some moisture tolerance against wet cleaning, have high resistance against carpet shrinkage (particularly when wet cleaned) and early bond strength development. All of this can be achieved with rubber resin systems.
However, the advance of acrylic polymers means that formulations with similar properties can be made. The main advantage to this is that you can get totally solvent-free products, as is usually the case in Europe, but the flip side is that site conditions and subfloor prep tends to need to be a lot better when using these products.
n Vinyl: When it comes to installing PVC (vinyl) floorcoverings then the use of a rubber resin adhesive is totally inappropriate. The material giving PVC its flexibility is called a plasticiser. To avoid chemical interaction and plasticiser migration occurring, a plasticiser resistant adhesive is needed.
This moves us away from rubber type products and towards the wide range of acrylic polymers and similar products which enable the vinyl adhesives to be tailored towards the end performance requirements.
The choice of high strength polymers with bond strength retention over a range of temperature enables us to manufacture ‘high temperature’ grade products. These are ideal for underfloor heating systems, conservatories, atriums etc.
They would be overkill, however, for a straightforward classroom or hospital ward where a high strength pressure sensitive (PS) polymer may be a better option, reinforcing the bond as it is trafficked.
Using a PS adhesive can also result in a thinner glue line or even an adhesive that can be trowelled and rolled to avoid reflection of trowel lines. However, using too soft a polymer may not prevent movement in the vinyl to allow shrinkage, so incorporating resins may also be necessary.
n Rubber: When it comes to rubber we no longer have the concerns of plasticiser but we do have to formulate adhesives with extremely high shear resistance. This is due to the inherent strength of rubber and its elastic qualities making it liable to lateral movement if not restrained by a suitable adhesive.
Historically this has meant the use of reaction products such as epoxy or polyurethane adhesives which are not the easiest products to use. Polymer technology now enables none reaction products to be used which give extremely high resistance to movement.
n Linoleum: Linoleum is a completely different animal to both rubber and vinyl. This is due mainly to the fact that it has a backing generally made of hessian/jute. Lino is again a very strong product so the challenge here is to provide an adhesive that gains strength very quickly to hold down any lino curl and resist any shrinkage but minimises water absorption into the backing.
The thinking behind this is that the hessian getting very wet will then begin to tension on drying out. Historically the adhesives selected were resin adhesives using alcohol as the solvent (resin alcohol) which offered added bonus of easy release.
Nowadays thankfully we can avoid solvents and utilise modern lino adhesives which can be high strength rubber resin system, acrylic or other copolymers of harder grades. The issue of plasticiser is not present with linoleum.
n Timber: Then there is timber. The main concern with timber is that it can move under variable room conditions and can be extremely forceful when it does so. Timber basically moves when its moisture changes through either absorbing extra moisture or drying out.
Room temperatures influence moisture conditions so don’t just think of cold wet days as the problem condition, dry summer days are just as bad. Traditional timber adhesives were solvent based, very high bond strength products which were okay for smaller dimension timber and engineered products but not so good with larger boards and solid timber.
The development of very high strength water-free elastic polymers such as MS polymers mean we now have high performance formulations for a wider range of timber floor types.
So, epoxy, polyurethane, acrylic, rubber resin, resin alcohol, MS polymers and so on are all utilised to make sure adhesives are up to the job. Technical needs along with handling requirements means that, as long as there is a range of floorcoverings, we as manufacturers and you as installers need to have a range of adhesives at your disposal.
Believe me, from a manufacture and stock control point of view we wish there wasn’t such a requirement too!
Martin Cummins is UK technical support manager at Bostik.
www.bostik.co.uk T: 01785 272625

This article has been reproduced from the Contract Flooring Journal. You can find them at www.contractflooringjournal.co.uk.