YING FIELD compound to ensure a long-lasting and attractive floor finish for every project.

high levels of foot traffic, a heavy-duty levelling compound should be selected for its high compressive strength which will create a durable surface for subsequently applied floorcoverings.

Such levelling compounds are a popular choice for preparing subfloors in retail settings, schools and hospitals. For example, the self-levelling properties and heavy-duty applications of F. Ball’s Stopgap 300 HD ensure a completely smooth and even base, helping floorcoverings withstand the demands placed on them.

OTHER LEVELLING COMPOUNDS There are a number of other particular situations when a levelling compound with additional features will be desirable.

When undertaking exterior flooring installations, it is important to choose a levelling compound that is suitable for outdoor use, to benefit from freeze/thaw resistant properties, for example.

Working over calcium sulphate screeds also requires special consideration. Calcium sulphate screed manufacturers advise that a calcium sulphate-based self-levelling compound is used to create a base for floorcoverings over this type of subfloor. The reason for this is that the application of cement- based products onto calcium sulphate screeds can result in a chemical reaction that causes the formation of ettringite, a crystalline material that can cause floor failure, where the two materials meet.

PRIOR PREPARATION Before a levelling compound is applied, the subfloor needs to be suitably sound, smooth and dry enough for the receipt of new floorcoverings. This may necessitate repairs to the subfloor or the removal of any surface contaminants and old adhesive residues (when not using a levelling compound that can be applied directly over the top).

F. Ball recommends that a moisture test is then conducted to determine subfloor moisture levels. Where a moisture test indicates that the relative humidity (RH) level within the subfloor is above 75% (65% if wood floorcoverings are to be installed), a waterproof surface membrane will be required to prevent floor failure.

The application of a primer is also required in almost all circumstances to promote adhesion of subsequently applied levelling compounds and stop the rapid drying of levelling compounds when applied over absorbent subfloors. It also prevents pinholing, caused by tiny bubbles resulting from the slow escape of air from the subfloor, which burst on reaching the surface, leaving small pinholes or craters as the levelling compound cures.

After these steps have been undertaken, the application of an appropriate levelling compound is the final stage in the subfloor preparation process before new floorcoverings can be installed. LEVELLING COMPOUNDS | 19

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