SPECIAL FOCUS: LEVELLING COMPOUNDS SMOOTH TALK


David Wilson, UK Technical Services Manager at Building Adhesives Ltd (BAL), offers a guide to subfloor preparation using levelling and smoothing compounds.


Levelling and smoothing floor compounds are designed to correct any surface irregularities within new and existing floor bases or to encase underfloor heating cables 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 additional materials. However, there are some exceptions on the market, such as BAL Level Max, which can be applied from 2 mm up to 80 mm (in localised areas) in one application without additional aggregates.


Conventional levelling and smoothing compounds are not designed to be used as a floor finish 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, fibre-reinforced products are particularly suitable i.e. BAL Level Max.


Fibre-reinforced and flexible products, such as BAL Level Max, are also particularly suitable for encasing underfloor heating cables and screeds containing underfloor heating because they can cope with movement of the background and thermal changes that occur.


A traditional, non-flexible, non-fibre reinforced levelling compound can crack if exposed to the same degrees of thermal change and associated substrate movement.


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 prevent 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 (DPM), such as BAL DPM.


When mixing your levelling compound, again follow the manufacturer’s instructions, including water to powder ratio, mixing speed and so forth. Once the correct consistency is achieved, pour the mix over the prepared substrate and spread to the required depth with a steel finishing trowel or long-handled blade. If you need more mixes, ensure these are blended in with the previous area.


Before allowing curing, ensure that the surface is sufficiently smooth to receive floorcoverings without any further treatment. If you are laying tiles or slabs, floors should be corrected to SR1 (Surface Regularity) – i.e. there should be a gap not exceeding 3mm underneath a 2-meter straight edge. We would not recommend the use of spiked rollers on a fibre-reinforced product (e.g. BAL Level Max) as this can pull fibres through to the surface. If any trowel marks remain, rub down before the compound has hardened.


Always allow the new floor to set before laying your finished floor surface. Setting times can vary depending on your chosen product and upon your floor finish. For example, an 80mm layer of BAL Level Max can be tiled after just 4 hours at 20°C and a minimum of 24 hours for other suitable soft flooring finishes. In the case of BAL Level Max in wet areas, allow a minimum of 24 hours before waterproofing with a suitable tanking system, such as BAL Tank-it.


Finally, we would always advise checking suitability with the product manufacturer to ensure compatibility for its intended purpose prior to application to ensure project success. At BAL, our Technical Advisory Service is fully equipped to provide support to contractors, architects and tilers using levelling and smoothing compounds – including NBS M40/M10/M20 specification assistance, on-site consultancy and expert technical advice.


www.bal-adhesives.com — 12 — www.tomorrowstileandstone.co.uk


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