ON THE LEVEL Here, David Wilson, UK Technical
Services Manager at Building Adhesives Ltd (BAL) provides an expert guidance
on subfloor preparation with levelling & smoothing compounds
Levelling and smoothing floor compounds are designed to correct any surface irregularities within new and existing floor bases and are available as either one-part or two-part products. Easily mixed and simple to apply, they are self- smoothing and are designed to achieve SR1 surface regularity for laying ceramic tiles or other floorcoverings.
In general levelling and smoothing compounds can be applied in thicknesses of up to 30-40mm but may require more than one application or with additional materials required. However, there are some exceptions on the market such as BAL Level Max which can be applied from 2mm up to 80mm (in localised areas) in one application without additional aggregates.
Conventional levelling and smoothing compounds are not designed to be used as a floor finishes and would require the use of a suitable wearing surface.
Typically; self-levelling and smoothing compounds are suitable for use with concrete, most screeds, including sand:cement, and calcium sulphate based screeds following the use of a suitable primer. However when levelling a rigid and stable timber floor, or screed containing underfloor heating, fibre- reinforced products such as BAL Level Max are particularly suitable. Remember to check the products you’re using with the manufacturer to ensure suitability for use.
Before laying a levelling and smoothing compound it is essential that correct preparation of the subfloor is carried out. Firstly ensure that the surface is clean, firm, dry and free from grease, dust and any other contamination which may be considered barriers to adhesion.
Any new concrete or screed must be left to fully cure according to the manufacturers’ instructions before applying any levelling and smoothing compound. Any direct-to-earth subfloors should incorporate an effective damp proof membrane. The majority of subfloors will also need priming before tiling.
When mixing your self-levelling and smoothing compound always ensure you follow the manufacturer’s instructions. BAL Level Max is mixed by adding powder to clean water in the ratio of five parts powder to one part clean cold water by weight. We would always recommend mixing with an electric drill mixer at a slow speed under 300rpm. Always mix until a lump-free mortar is achieved and allow the mixed leveller to stand for two minutes before re-mixing for 30 seconds.
Once the required consistency is achieved, pour the mix over the prepared substrate and spread to the required depth using a suitable steel finishing trowel or long handled blade. Work the mixture well into the corners, edges and around projections. When you’ve finished spreading the mixture on
twitter.com/TContractFloors SUBFLOOR PREPARATION | 43
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