Neil Sanders, technical director at F. Ball and Co. Ltd., the UK’s leading manufacturer of subfloor preparation products and adhesives for floorcoverings, advises on preliminary work to achieve optimum results when installing floorcoverings as part of a refurbishment.
The first step in any flooring installation should be to check that subfloors are suitably sound, smooth and dry. When undertaking installations as part of a refurbishment, you never know what you are dealing with until you actually remove old floorcoverings. There will frequently be a number of challenges that you would be less likely to encounter in new-build settings, including contending with subfloors in a poor condition. Just as when installing floorcoverings anywhere else, flooring contractors need to be aware of the problems posed by the common problem of damp, the leading cause of floor failure.
Moisture management
Excess levels of subfloor moisture can result in moisture rising up and attacking adhesives and floorcoverings, possibly causing complete floor failure. Building regulations introduced in 1965 made it a legal requirement to install a structural damp-proof course in new buildings, so excess subfloor moisture as a result of rising damp is more likely to be a concern in buildings built before this time.
Even if a damp-proof course is present, contractors should always conduct a moisture test to determine subfloor moisture levels before proceeding to apply subfloor preparation products, not least because the damp-proof course may have been compromised at some point in the building’s history. Where a moisture test indicates that subfloor relative humidity (RH) levels are above 75% (65% if wood floorcovering will be installed), a waterproof surface membrane will be required to suppress excess subfloor moisture levels.
Epoxy waterproof surface membranes are available that will isolate excess subfloor moisture caused by rising damp and residual construction moisture where relative humidity values are up to 98%, with a single coat application, and fully cure in as little as three hours.
Damaged subfloors
Upon removing old floorcoverings, contractors may discover that the subfloor is cracked or damaged. This needs to be addressed before proceeding to the next stages of subfloor preparation. The appearance of cracks should always be investigated in case there is an underlying issue that may result in floor failure. Where subfloors are very badly damaged, mechanical repair of the subfloor may be necessary. In most cases, cracks as deep as 50mm can be filled with a repair compound. Some levelling compounds can also be filled up to 50mm when graded aggregate is added.
It may also be the case that contractors find a sand/cement or calcium sulphate screed has a weak or friable surface – often the result of improper installation or curing techniques.
To avoid having to completely remove a weak or friable screed by mechanical means, it may be possible to treat it using a surface reinforcement system, such as Stopgap SRS, a two-component epoxy resin reinforcement material designed to quickly stabilise and reinforce weak sand/cement or calcium sulphate screeds. Contractors simply mix the components thoroughly, pour the mixture over the weak subfloor and spread out with a rubber squeegee, working into the surface until no more liquid is absorbed. Stopgap SRS is fast-acting, meaning weak screeds can be reinforced overnight to provide a base suitable for the installation of subsequent subfloor preparation products.
Contamination
Old adhesive residues, such as bitumen and carpet tile tackifiers, may also be present after removing old floorcoverings. Traditionally, contractors would have to remove these completely by mechanical means before proceeding. Recent innovations now offer an alternative time-saving solution: as long as adhesive residues are minimal and well bonded, contractors can apply a smoothing underlayment that has been specially formulated for use over old adhesive residues.
Such products were previously only available in bag and bottle formulations. The latest advancements in technology have enabled F. Ball to create a new fast-track, water-mix smoothing underlayment that can be applied over old adhesive residues, Stopgap 1500 AquaPro.
Subfloors may also be contaminated with oil, grease or other chemicals. In this case, the surface will need to be removed using mechanical means before applying other floor preparation products. In the case that the subfloor is very badly contaminated, the screed may need to be completely replaced. An alternative, where a fully bonded system is not required, is to install F. Ball’s Stopgap Isolator Membrane, an impervious loose-lay sheet that can be laid over damp or contaminated subfloors prior to the installation of vinyl sheet, linoleum or rubber floorcoverings and bitumen backed carpet tiles.
Next steps
Once the subfloor is suitably sound, smooth and dry, contractors can proceed with the installation of new floorcoverings. Where an isolator membrane has not been used, this should include the application of a suitable levelling compound to create a perfectly smooth base for the receipt of floorcoverings.