THE COMPLE
Here, we present some expert advice on membrane as well as a rec
SECURE YOUR FLOOR Is it always necessary to lay a damp-proof membrane before
applying smoothing underlayments? Martin Cummins, UK Technical Support Manager at Bostik explains.
Laying new flooring onto a subfloor that has a moisture rating above 75% relative humidity (RH) can lead to a plethora of problems. Therefore it pays to apply a surface damp- proof membrane (DPM).
The types of floorcoverings used in many modern buildings, such as rubber and highly flexible vinyl, were not prevalent years ago. They have a much lower moisture vapour transmission rate than the less flexible products used in the past, in particular old thermoplastic tiles. As a consequence, they will entrap moisture beneath them on damp floors if no surface DPM is used.
The adhesives used to bond these more modern floorcoverings are also less tolerant of moisture than the older, solvent-based, and in particular bitumen-based adhesives. This means you’re left with a flooring system that is much more sensitive to moisture levels in the subfloor.
If a subfloor has a Relative Humidity (RH) reading in excess of 75%, a surface DPM can be used to suppress the residual moisture, therefore protecting the smoothing compounds, adhesives and floorcoverings above.
A major argument for the use of a surface DPM in modern applications is the speed in which buildings are now built and, more importantly, how quickly they receive a floorcovering. Fast track building projects generally result in subfloors still retaining a large amount of residual moisture, for example from moisture not used in the reaction of binders and so on, at the time that the flooring is to be laid.
Historically buildings were not put up at the rate of today, so residual moisture was not so much of an issue; however in my experience the flooring contractors of today won’t risk not using a DPM on prestigious jobs unless the main contractor gives an instruction to do so.
The use of a surface DPM has been fundamental in reducing the amount of complaints of floor failures in the market. I cannot categorically state that floors above 75% RH will cause a failure but there is risk involved as soon as these levels are exceeded. If they’re being totally honest, most main contractors, manufacturers and flooring contractors will admit to having a job or two where failures have occurred due to moisture levels in the subfloor.
The science behind the use of a DPM goes beyond wet causing bubbles in the floor. It involves moisture vapour transmission rates, alkalinity, and density of subfloors, as well as the effects of plasticisers and other materials in floorcoverings. The level of moisture testing equipment in the market and the quotes in all the standards, including those from ASTM, suggests that the academics have observed a potential problem and are offering solutions.
So, in summary, if you want belt and braces protection to ensure longevity and performance for your next flooring installation, be sure to use a DPM.
34 | SMOOTHING UNDERLAYMENTS
www.tomorrowscontractfloors.com
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