34 Structural Elements Dealing with damp


Stephen Boulton at F. Ball & Co. Ltd. provides crucial advice to guard against the problems caused by excess subfl oor moisture when installing fl oor coverings.


U


nchecked subfl oor moisture, whether residual construction moisture or rising damp, can attack fl ooring adhesives and fl oor coverings, causing wood to warp and damaging textile fl oor coverings by


promoting mould and bacterial growth. Not only can this ruin the fi nished appearance of a fl ooring installation, but it can potentially cause fl oor coverings to ‘debond,’ resulting in complete fl oor failure and present a health hazard. We frequently receive enquiries from contractors who have been called to


rectify a recent fl ooring installation where fl oor coverings have begun to liſt as a result of unmanaged excess subfl oor moisture, and our regional technical representatives oſt en attend site visits where this is the case. To prevent fl oor failure due to excess subfl oor moisture, it is important to


take time to determine subfl oor moisture levels and deploy an appropriate moisture management solution, where necessary, before installing fl oor coverings in a project.


TESTING We recommend that a moisture test be undertaken as part of any fl ooring installation, having fi rst prepared the subfl oor so that it is suitably smooth, sound and free of contaminants. If the subfl oor Relative Humidity (RH) levels exceed 75% (65% if wood fl oor coverings are to be installed), a moisture management solution will be required to prevent excess subfl oor moisture from attacking adhesives and damaging fl oor coverings. A quick, non-intrusive way to identify the presence of subfl oor moisture


is to use a handheld radio frequency moisture meter. If the device indicates the presence of moisture in the subfl oor, further testing will be required to determine the precise subfl oor relative humidity levels and whether a moisture management solution is required. T e only method of measuring subfl oor relative humidity levels with


certainty, and the method advocated by British Standards, is to use a calibrated hygrometer. T ese devices measure the relative humidity of a small volume of confi ned air in equilibrium with the subfl oor, taking into account the ambient temperature. T e device is affi xed to the subfl oor using butyl tape to create an airtight


seal around the base of the instrument. It is then leſt for a suffi cient amount of 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 aſt er leaving the instrument overnight, and readings taken four hours apart are identical. It is recommended that multiple digital hygrometers be placed at regular intervals across the entire subfl oor area to avoid the prospect of localised excess moisture not being detected.


WATERPROOF SURFACE MEMBRANES T ere are a number of options available to contractors for creating a barrier to protect the fl oor covering from high levels of moisture detected within the subfl oor. T e application of a liquid waterproof surface membrane is the usual solution


for eff ectively controlling damp. T e best performing epoxy waterproof surface membranes will isolate excess subfl oor moisture where relative humidity values are up to 98%, with a single coat application, which will fully cure in as little as three hours.


It is important to take time to determine subfl oor moisture levels


Digital hygrometers affi xed to the subfl oor at regular intervals to accurately measure subfl oor relative humidity (RH) levels


Quicker, two coat, water-based systems are also available that will create an


eff ective barrier against residual construction moisture where relative humidity values are up to 95%. T e fi rst coat cures in 15-20 minutes. A further 30 minutes of curing time is required for the second coat.


AN ALTERNATIVE SOLUTION An alternative solution for dealing with damp is available for situations where a waterproof surface membrane cannot be applied. T is may be the case where fl ooring installations are part of a refurbishment project and screeds are contaminated with oil, other chemicals or old adhesive residues. It is also useful in heritage settings where the subfl oor must be preserved. In these situations, a loose lay isolator membrane can be laid directly onto the


subfl oor, without the requirement for an adhesive, to provide a barrier to stop excess subfl oor moisture from causing fl oor failure. T ese membranes typically have 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 fl oor coverings can be adhered to its upper surface. T is enables durable new fl oors to be installed and easily removed at a later date, allowing buildings to be returned to their original state and off ering a solution for temporary fl ooring installations.


NEXT STEPS When a suitable moisture management solution is in place, contractors can proceed with preparing the subfl oor for the installation of new fl oor coverings. Where an isolator membrane has not been used, this should include the application of a smoothing compound to create a perfectly smooth base for the receipt of fl oor coverings, remembering to prime beforehand if necessary. Contractors can proceed to install fl oor coverings using an appropriate


adhesive once the smoothing compound has cured. At this stage, the compatibility of particular fl oorcoverings and adhesives should be checked to further ensure against fl oor failure. To do this, contractors can consult the manufacturers’ Recommended Adhesives Guide or see the fl oorcovering manufacturers’ instructions.


Stephen Boulton is the technical service manager at F. Ball & Co. Ltd Housing Management & Maintenance August/September 2025


Flooring Feature


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36