Moisture considerations

The floor must be sound and relatively level, but also it is important that it is free from excessive moisture content. Ground floors with a concrete sub floor, and in particular basements and cellars, should have a Damp Proof Membrane (DPM) on the sub floor - either a full 1000 gauge DPM sheet or a liquid DPM Primer such as Sikabond MB Primer.

Always err on the side of caution where moisture is concerned. Wood flooring can be bonded directly to concrete, but only where the moisture content of the concrete is below 5%.

While old concrete sub floors are at risk from rising damp, new concrete screeds are also a problem because a typical screed to take about 90 days to dry to the required level. (However, many factors can affect the actual timings.)

On new builds it is sensible to ensure that the relative humidity is not too high or low - ideally it wants to be between 45-60%. This can be affected by factors including wet trades, plastering etc, which as well as the fitting of windows must be completed and dried out well before contemplating wood floor installation.

In fact, it is a good idea to leave the installation of the flooring as late as possible in the project plan. Consider it in the same way as carpeting to avoid unnecessary damage to the surface during completion of works by other trades.

We recommend that the sub floor be treated with a damp proof solution underneath hardwood boards to prevent moisture causing excessive expansion and contraction in the floorboards - or use a moisture meter to ensure that the level is 5% or less.

Alternatively, place a plastic sheet firmly over the floor for 4-5 days. If there are water droplets underneath the sheet, or if the concrete has turned a darker colour, then the floor is too moist.

If in doubt, obtain a moisture meter or install a DPM sheet or liquid MB primer before fitting wood flooring. This may increase the project budget, but is better than having the wood flooring come up - and depending on the flooring chosen it's only a fraction of the overall cost.

> back a page