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The sound of silence: getting the most from acoustic flooring and underlays

Life can become a lot more comfortable by using acoustic and underlay systems and choosing the right adhesives to install them correctly says Martin Cummins.

THE traditional picture of urban living, ranging from terraced housing through to detached mansions, has gradually changed over time. Mainly driven by the shortage of space as well as affordability, we now find more shared accommodation in the form of split-level house purchasing, and also a massive increase in apartment living. In turn, this has led to greater consideration for how to keep noise transfer within properties at a minimum as mental wellbeing in shared buildings is a very important factor these days. Already, many design features are being incorporated into new buildings to minimise the transfer of sound.

From a flooring point of view we have one simple task: can we reduce the noise from footfall that transmits to other occupants in a property? The simple answer is ‘yes’ and the industry has been doing this for a considerable time anyway. The UK traditionally favours soft carpet and the various thicknesses and sound deadening attributes of underlays. By its nature, carpet dissipates and absorbs a considerable amount of sound and, when coupled with a high level of sound insulation (referenced in decibels (dB)), it can give a very effective acoustic barrier.

Underlay and carpet systems are traditionally referred to as double-stick installations and, when bonding them to a subfloor for improved performance, you need to consider what the most appropriate adhesives are. If you’ve ever had to rip up an old underlay that has been ’permanently’ bonded, you’ll have discovered the underlay generally ends up being ripped apart and needs to be scraped off the floor – a big job indeed.

Rather than give a full strength bond to the floor, you can use an adhesive designed to tack the underlay in place. This enables the covering to be readily uplifted relatively cleanly and with much less effort for you, the client, or a future installer – which could well be you again! These adhesives need a high degree of dry bond performance and are generally pressure sensitive (ie the bond improves with footfall which applies pressure).

Most underlays will have a very low or non-absorbent core to them. This means any adhesive being used to bond the carpet to the underlay will not be absorbed into the latter. Some underlays do have a crepe paper surface that gives a small amount of absorbency, which can be a great help. The adhesive will need to have excellent grab at the point the carpet is being laid, especially with lightweight and ’boardy’ carpets. This can be achieved by giving a ’tack off’ time and still maintaining a strong enough bond, if the adhesive is designed in this manner. Adhesives with a small amount of solvent in them can give a much quicker onset of tack, simply due to the faster evaporation rate of solvents compared to water.

However, as an industry we need to consider moving away from solvents so may need to change our practices as well as our products. Provided the carpet can breathe and the adhesive is non-staining, there can be greater bond strength built up over time as the adhesive continues to dry out.

I’m sure you all know the types of adhesives being referred to above as they are pretty much industry standards. However, when coming to other floor coverings – primarily vinyl, the picture changes somewhat. The acoustic flooring systems are generally a lot firmer and, with there being a higher degree of grip to the floor when walking on vinyl flooring, it’s beneficial to bond the acoustic underlay far more strongly than you would a traditional underlay. A tackifier/PS type adhesion may not suffice, so you should consider a more robust adhesive.

Bonding the vinyl onto an acoustic floor does create a new problem. If you lay onto the adhesive whilst in its wet phase, you risk trapping moisture between the vinyl and acoustic layer and this never drying, so the bond strength will never build up.

An adhesive that offers a high bond strength when most of its moisture has escaped is the perfect choice. Perhaps a fully dry stick product can be used, but be careful with LVT products, which are extremely strong and will be prone to dimensional change that the dry stick’s pressure sensitive characteristic is sufficiently strong in shear strength to prevent gapping or tenting of the LVT. With sheet vinyl or other sheet products that can be deemed stable, a pressure sensitive adhesive can do the job.

As it is vinyl and has plasticiser in its make up, you’ll need to avoid using the likes of SBR adhesives and only use acrylic systems. You should also avoid products containing solvents as the solvents will linger and potentially stain the flooring.

As an installer, you’d probably – and ideally – prefer one adhesive to do both the bonding of the underlay or acoustic layer and the floorcovering above. At this moment in time the product selection with carpets will be two different products: a tackifier type for the underlay and a high grab type (though not necessarily an acrylic) for the carpet.

With vinyl, however, it’s possible to develop an adhesive with all the characteristics required, including strong wet grab, plasticiser resistance and high strength dry stick, as is the case with Bostik STIX A740 MULTI BEST. You’ll have to use it in a different way for the two different applications with regard to open time, and possibly trowel size, but at least you only need one adhesive in the van.

Finally, there needs to be a consideration as to how to deal with wood flooring.

There may be limited opportunity to utilise an underlay/acoustic layer under a timber floor, except if it’s a looselay laminate type, but the nature of the adhesive used to bond timber can significantly help the acoustics. Because the adhesive bed with timber is thicker than vinyl and carpet, we can develop adhesive that’ll give a level of noise reduction.

This is quite common in Europe and the US. By using a 100% solids adhesive you don’t need to allow the product to dry or tack as it will react and cure regardless. This means all the adhesive applied is playing a part in the performance of the acoustics, and with hybrid polymer products this can be significant. They’re flexible, have excellent recovery under load and offer extremely high bond strength – all the properties needed for timber with sound absorbency characteristics. Of course, you can spend more and use a specific system that gives declared dB reductions if that’s required.

Sadly, neither I nor Bostik can help if you have inconsiderate and noisy neighbours. But for those who haven’t, life can become a lot more comfortable by using acoustic and underlay systems and choosing the right adhesives to install them correctly.
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