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HomeHelp and adviceBetween hell and excess moisture

Between hell and excess moisture

Jason advises on guarding against floor failure as a result of excess subfloor moisture, including the use of moisture management solutions.

UNCHECKED excess subfloor moisture, whether residual construction moisture or rising damp, can attack adhesives, causing floorcoverings to de-bond, wood to warp and damaging textile floorcoverings by promoting mould and bacterial growth, ruining the finished appearance of an installation and potentially leading to floor failure. The breakdown of adhesives as a result of contact with moisture can also cause increased VOC emissions in indoor environments.

Excess subfloor moisture is the leading cause of floor failure and results in major inconvenience and losses for contractors year after year. F. Ball’s technical service department frequently receives calls from contractors who have been called to rectify a recent flooring installation where floorcoverings have begun to lift as a result of unmanaged excess subfloor moisture, and our tech reps often attend site visits where this is the case.

To prevent this, contractors should always take the time to determine subfloor moisture levels and deploy an appropriate moisture management solution where necessary.

Moisture test
F Ball recommends that contractors undertake a moisture test as part of any flooring installation, once it is established that the subfloor is suitably smooth, sound and free of contaminants. If the Relative Humidity (RH) levels in the subfloor exceed 75% (65% if wood floorcoverings are to be installed), a moisture management solution will be required to prevent excess subfloor moisture attacking adhesives and damaging floorcoverings.

A quick, non-intrusive way to identify the presence of subfloor moisture is to use a handheld radio frequency moisture meter. If the device indicates the presence of moisture in the subfloor, further testing will be required to determine subfloor relative humidity levels and the requirement for a moisture management solution.

The only method of measuring subfloor relative humidity levels with certainty, and the method advocated by British Standards, is to use a calibrated hygrometer. Affixed to the subfloor using butyl tape to create an airtight seal around the base of the instrument, these devices measure the relative humidity of a small volume of confined air in equilibrium with the subfloor, taking into account the ambient temperature.

When using a hygrometer, it’s important to leave sufficient time to allow entrapped air to reach moisture equilibrium with the screed or base before the unit is switched on. Equilibrium can generally be assumed after leaving the instrument overnight and readings taken at four-hour intervals show identical readings.

Waterproof surface membranes
There are a number of options available to contractors for creating a barrier to protect the floorcovering from high levels of moisture detected within the subfloor.

The application of a waterproof surface membrane is the usual solution for effectively controlling damp. Advanced products are now available, such as F Ball’s Stopgap F77, that will isolate excess subfloor moisture where relative humidity values are up to 98%, with a single coat application, which will fully cure in as little as three hours.

F Ball’s Stopgap F78 provides an even quicker, two-coat system. The first coat cures in 15-20 minutes, and a further 30 minutes’ curing time is required for the second coat, meaning an effective barrier against residual construction moisture where relative humidity values are up to 95% can be created in less than two hours.

Alternative solutions
An alternative solution for dealing with damp is available, where a waterproof surface membrane cannot be applied. This may be the case where screeds are contaminated with oil, other chemicals or old adhesive residues, as well as in heritage settings where the subfloor must be preserved.

In these situations a loose-lay isolator membrane, such as Stopgap Isolator Membrane, can be laid directly onto the subfloor, without the requirement for an adhesive, to provide a barrier to stop excess subfloor moisture causing floor failure.


The membrane has nodules on the underside, creating an airspace to allow water vapour to travel to the edge of a room, into a dry wall or ventilated area, where it can safely escape. A wide range of floorcoverings can be adhered to its upper surface.

By acting as a base to receive resilient floorcoverings and carpet tiles, Stopgap Isolator Membrane allows durable new floors to be installed and easily removed at a later date. Thus, allowing buildings to be returned to their original state, offering a solution for temporary flooring installations.

Next steps
Once a suitable moisture management solution is in place, contractors can proceed with preparing the subfloor for the installation of new floorcoverings. Where Stopgap Isolator Membrane has not been used, this should include the application of a levelling compound to create a perfectly smooth base for the receipt of floorcoverings.    
www.f-ball.co.uk

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