FLEXIBLE SUBFLOORS
Stephen Boulton, technical service manager at F. Ball and Co. Ltd., gives his guidance on installing floorcoverings over flexible substrates.
Subfloors, such as metal and plywood, can move when subject to normal foot traffic. They also expand and contract naturally as a result of fluctuations in temperature. These movements can cause cracks in general purpose levelling compounds, and these can begin to show through floorcoverings over time and can possibly result in eventual floor failure. For this reason, manufacturers of subfloor preparation products have developed specialist flexible levelling compounds to create a suitable base for the receipt of floorcoverings when working over flexible subfloors. As well as opting for this type of levelling compound in these situations, contractors should follow best practice when preparing the subfloor beforehand.
PRIOR PREPARATION Before undertaking any flooring installation, it’s important to ensure that the subfloor is suitably sound, smooth and dry.
Plywood overlays should be securely fixed to the subfloor, ensuring that the plywood is screw-fixed at regular centres in accordance with the CFA guidelines. Joints should be effectively supported to prevent any vertical displacement when loaded. When applied as part of a refurbishment, all traces of old adhesive residues should be removed.
It is highly recommended that contractors undertake a moisture test to determine subfloor relative humidity (RH) levels before proceeding with preparations. Where subfloor relative humidity levels are above 75% (65% if wood floorcoverings are to be installed) a moisture management solution will be required to stop potential floor failure.
It is also essential to prime the subfloor. Priming promotes the adhesion of subsequently applied levelling compounds onto non-absorbent subfloors and stops levelling compounds drying too rapidly, resulting in a reduced working time and wet edge when applied over absorbent subfloors. It also helps to prevent pinholing, caused by tiny bubbles resulting from the slow escape of air from the subfloor, which burst on reaching the surface, leaving small pinholes as the levelling compound cures.
Where flexible subfloors are made up of panels, in raised access floors for example, spaces between these should be filled with a suitable floor finishing compound, such as F. Ball’s Stopgap 500 Micro, prior to the application of a levelling compound. This is so that the gaps do not transfer to
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imperfections in the appearance of the finished installation. For these purposes, cement-based primers, including F. Ball’s Stopgap Fill and Prime, are available that fill the gaps between flooring panels while priming the subfloor at the same time.
FLEXIBLE LEVELLING COMPOUNDS Once the subfloor has been prepared and primed, contractors can proceed to applying a flexible levelling compound to create a perfectly smooth base for floorcoverings. Stopgap 700 Superflex was developed by F. Ball especially for this purpose.
Stopgap 700 Superflex is reinforced with tiny fibres that maintain the integrity of the levelling compound, preventing cracks from forming as a result of subfloor movement. These act like steel rods in reinforced concrete, ensuring that the installation retains its strength despite the stress caused by foot traffic or temperature fluctuations. It is suitable for application over plywood and steel subfloors, including raised access panels, as well as concrete and sand/cement screeds.
F. Ball’s flexible levelling compound is also fast setting. It is walk on hard just 60 minutes after application and allows floorcoverings to be installed in as little as three hours, while maintaining a working time of 20–30 minutes, making it ideal for projects where time is tight and reduces the time that areas are out of use. The levelling compound is also protein-free, meaning that it is suitable for use in biologically sensitive areas such as laboratories and hospitals, and is also approved for marine use.
APPLICATION TIPS Stopgap 700 Superflex is self-smoothing, so minimal trowel work is required, while the use of a spiked roller is recommended to dispel any air trapped inside the levelling compound, minimising the chance of pinholing occurring and creating a smooth, even finish.
Contractors can then proceed to installing chosen floorcoverings, remembering to check floorcovering-adhesive compatibility. Following the steps outlined here will ensure the integrity and appearance of a flooring installation for many years to come, avoiding costly remedial work and saving valuable time and money.
www.f-ball.com/en
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