Carpet Underlay

Carpet Underlay Purpose - wear; comfort

What actually causes wear on carpets? It is the imperceptible movement of it as your steps grind it against the hard sub-floor. With each footstep the pile is skewed one way or the other, commonly in the same direction. This skewing of the pile is the start of wear and at minimum causes unsightly shading (almost like wet patches).

The main purpose of carpet underlay is to provide the carpet with extra wear during its lifetime. Modern carpets rarely wear out - people want their carpets to stay looking good for longer and to feel comfortable. It is by reducing this grinding into the hard sub-floor (concrete or floorboards) that carpet underlay reduces wear.

Thickness - spongy; firm

It is a misconception that thicker, spongier underlays mean better wear when it comes to carpet underlay. Spongy underlays (especially ribbed rubber) allow the carpet more movement against the hard sub-floor as it moves up and down.

The thicker and softer that spongy rubbers are, the greater this detrimental movement. It was once said by a well known and respected Cheltenham carpet fitter that carpet would probably give the most wear if it was stuck directly to the floor with no underlay at all, because it moved less.

Therein lies the source of the problem. Buyers were trained to prioritise comfort above practicality, so the underlay fashion for the most part of the 20th Century was shaped by thick and spongy underlays. This was reinforced by the immediate gratification of a the client, a marketing man's dream.

Firmer is better - urethane foam; crumb rubber; natural felt

Up-to-date thinking now accepts that the firmer underlays (urethane foam) with a thickness of about 8 - 10 mm maximum will reduce the grinding effect against the sub-floor, consequently giving carpets prolonged appearance retention. The luxurious feeling will only feel marginally less "deep" than ribbed rubber underlays.

Two exceptions to the firm foam school of thought are crumb rubber and natural felt, or a combination of both (Duotex). These underlays will also reduce the detrimental movement of carpet friction against sub-floors because they are also firm.

Another benefit of firm underlays is that they also reduce furniture indentations.

Natural flooring - firm; double stick

Natural flooring like coir, seagrass and sisal require underlay that can be adhered to the sub-floor and then receive adhesive to stick the flooring directly to it. If the sub-floor is timber or board, then a conventional firm carpet underlay can be used as it is stapled down.

If however the sub-floor is hard and consequently the underlay cannot be stapled, then a two sided face will be necessary to the underlay so it can be fixed with a tackifier adhesive. Natural flooring requires a firm foam underlay (suitable for double sticking).

Underfloor heating - tog rating

When underfloor heating has been installed, the underlay will have to have a low "Tog rating" of between 0.5 - 0.8. The underlay Tog rating has to be added to the Tog rating of the carpet.

Useful links for underlay

Woodward Grovesnor - respected Division of Brintons; excellent guide to underlay

Completely Flooring - buy underlay online

Trade Priced - buy underlay online

The Carpet Underlay Company - buy underlay online

Sound Service - noise insulation underlay (great for flat tenants suffering snoring from other flats)

CMS Acoustic Solutions - acoustic underlay; get samples; downloads

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