Floor Preparation

A new floor can only ever be as good as the surface beneath it. Unevenness telegraphs through thin materials such as LVT, trapped moisture can cause adhesive failure, cupping or mould under wood and carpet alike, and old adhesive residue can prevent a new floor bonding correctly. Preparation is where the long-term success of the floor is actually decided, well before the visible finish is laid.

Relative humidity, or RH, testing measures the moisture condition inside a concrete subfloor, expressed as a percentage. In plain terms, a calibrated hygrometer probe is inserted into the slab and left to equilibrate, and the reading tells us whether the subfloor is dry enough for the chosen flooring and adhesive system. Many wood and adhesive manufacturers specify a maximum RH percentage before their products can be warranted, so this is not a precaution we take lightly, it is often a condition of the flooring's own guarantee.

Readings that come back too high do not mean a floor cannot proceed, but they do mean either further drying time or a suitable damp-proof membrane is needed before installation, and we explain the implications of each option clearly.

Once existing coverings are uplifted, we inspect the subfloor for cracking, hollow-sounding areas, general flatness and any residue from previous adhesives. Timber subfloors are checked for movement, deflection and secure fixing, while concrete slabs are checked for level and surface integrity. This assessment determines whether smoothing compound, plywood overlay or localised structural repair is the right route.

Smoothing compound, or self-levelling screed, is a pourable cementitious product used mainly on concrete subfloors to correct minor unevenness and create a flat surface for adhesion. Plywood overlay is typically used over timber subfloors, or where a floating floor system needs a stable, uniform base, and works by bridging small movements in the boards beneath rather than being a liquid-applied fix. The right choice depends on subfloor type, the flooring being installed, and the extent of unevenness found.

This varies considerably depending on what is found. Uplift and assessment can often be done in a day for a typical room, but smoothing compound needs proper curing time, generally at least a day and often longer depending on depth and ambient conditions, and any damp-proof membrane or additional drying required for elevated moisture readings can extend the programme by several days. We build realistic drying times into the overall project schedule rather than rushing this stage, since doing so risks the entire installation.

Not every adhesive suits every combination of subfloor and flooring material, and using the wrong one can lead to poor bonding, staining through the finished surface, or failure under underfloor heating. We select adhesives based on subfloor moisture condition, flooring type and, where relevant, underfloor heating specification, in line with manufacturer requirements, rather than defaulting to a single product for every job.