SURFACING
SUBFLOOR PREPARATION TO AVOID FLOOR FAILURE Failing to undertake proper subfloor preparation before the application of new floorcoverings can result in an unsightly finish or even complete floor failure, leading to costly remedial work. Fortunately, this can be avoided by adhering to just a few basic principles of subfloor preparation, including the need to guard against excess subfloor moisture – the leading cause of subfloor failure. Stephen Boulton, Technical Service Manager at leading manufacturer of subfloor preparation products, F. Ball and Co., goes through these processes. F. BALL AND CO.
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lthough it should be standard practice, there is still a lack of awareness regarding the need to undertake certain procedures before installing floorcoverings and often this results in lost time and unforeseen expenditure. Ensuring a longlasting, visually attractive finish involves following a few other basic steps, including making sure the subfloor is in a suitable condition before work begins, applying a levelling compound to ensure a perfectly smooth base for the receipt of floorcoverings and remembering to prime beforehand.
Subfloor preparation The first step in any flooring installation is to make sure the subfloor is suitably sound and smooth. If the subfloor is a newly-installed screed, contractors will need to ensure that any laitance – the crust of cement and fine aggregates that form on the screed’s surface as it dries – is ground off. The typical method of removing laitance is using a rotary sanding or abrading machine. If the project is part of a refurbishment, the subfloor’s condition will need to be assessed once old floorcoverings have been removed. You may discover that the subfloor is cracked or damaged, in which case, it will require extra preparation. In most cases, you can fill cracks as deep as 50mm with a floor repair compound. Subfloors may also be contaminated with oil, grease or other chemicals, necessitating mechanical preparation by grinding or abrading before applying other floor preparation products. Old adhesive residues will need to be removed mechanically unless a levelling compound suitable for use over old adhesive residues is used. FC&A – FEBRUARY – 2021
Moisture test Contractors need to be particularly aware of the problems posed by excess subfloor moisture in the base. Whether the result of rising damp or residual construction moisture, unmanaged subfloor moisture can attack adhesives and floorcoverings, possibly causing complete floor failure. For these reasons, F. Ball and Co. recommends that a moisture test is conducted to determine subfloor relative humidity (RH) levels as part of any flooring installation. The only method of measuring subfloor RH levels with certainty and compliance with British Standards is to use a calibrated digital hygrometer. Where a moisture test indicates that subfloor RH levels are above 75% (65% if a wood floorcovering will be installed), a moisture management solution will be required to suppress excess subfloor moisture levels and prevent floor failure. 28
