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Commercial Flooring News

Fail To Prepare, Prepare To Fail

David Gatfield with golden rules on surface preparation
FROM screeds to DPMs and smoothing compounds, here are the golden rules of subfloor preparation.
Everyone knows, or at least should know, that correct preparation is key before successfully completing any task, whether it’s DIY at home or the smoothing and levelling of a subfloor before installing a floorcovering.
All subfloors that are to receive vinyl, rubber, contract carpet or linoleum must be prepared to a good standard if problems are to be avoided. There are a few things to consider before starting work, most are obvious such as whether the floor will need screeding or not.
But some are less apparent and can trip up the unwary. Post-installation problems can mean costly remedial work, which can reduce or eliminate any profit you may have made on the installation.
The first thing to assess, particularly if it’s a ground floor installation, is the approximate age of the building. Anything built prior to the mid 1960s is very unlikely to have an integral DPM.
Even if the existing flooring shows no signs of damage, it can’t be taken for granted that when the new one is installed, moisture related issues won’t occur. That will be a problem you have inherited.
The golden rule is always to carry out a moisture test, even a non-intrusive surface reading is better than none at all; it will at least give an indication of whether a more in depth survey should be carried out.
In general terms it’s the joint responsibility of the main contractor and the flooring contractor to ascertain whether or not a subfloor complies with BS 8203 and is suitable to receive the finished floorcovering. This includes testing for the presence of moisture.
If there’s no main contractor, it is the sole responsibility of the flooring contractor to satisfy themselves that the subfloor is suitable before proceeding.
If there is moisture in excess of 75% RH, you should seriously consider providing a surface, liquid DPM to protect any subsequent flooring installation from moisture up to a maximum of 97% RH.
As an alternative you might consider a loose lay safety flooring such as Altro XpressLay, which can also be used over damp or green subfloors to the same upper RH limit as quality surface DPM systems. Check out Peter Daulby’s technical article in CFJ last month for a more detailed look at how moisture impacts on flooring installations.
Smoothing compounds, though all grey in colour, can be streets apart when it comes to quality. Some are compressively weak, as little as 10/11 Newtons per mm squared, even if they’re properly mixed, leading to indentations through the vinyl if heavy loads or hospital trollies are rolled over the finished floor.
Others can be as strong as 20/25 Newtons and such products can be used under heavy duty flooring, for example in bank vaults where money weighing hundreds of kilos is transported on steel wheeled trucks.
Yet more are fibre bonded, and are routinely specified for the overlaying of ventilated wooden floors, and others so compressively strong at over 30 Newtons that they can be used under heavy duty resin flooring without fear of failure.
Giving due consideration to the preparation before starting the contract will save you time and money in the long run, and avoid any nasty surprises down the line.

David Gatfield is Altro regional technical services manager
T: 01462 489405

This article has been reproduced from the Contract Flooring Journal website. You can find them at