F. Ball provides expert advice on dealing with weak or friable screeds as part of a refurbishment.
REPAIR AND RENEW
Installing floorcoverings as part of a refurbishment project involves a series of steps: old coverings are first removed along with any old adhesive residues or contaminants before the subfloor is prepared for the installation of a new product. Sometimes, upon removing old floorcoverings, contractors may discover that the base below is weak or friable – the result of poor installation or curing techniques. This must be dealt with before the installation can proceed.
Traditionally, a weak or damaged screed would have to be entirely removed by mechanical means and a new screed installed before the refurbishment could proceed. Now, contractors have a less costly and disruptive option: in most cases, a weak or friable screed can be prepared with a surface reinforcement system (SRS).
SURFACE REINFORCEMENT SYSTEMS One such system, F. Ball’s Stopgap SRS, is a two-component epoxy resin reinforcement material designed to quickly stabilise and reinforce weak sand/cement or calcium sulphate screeds and is suitable for use over underfloor heating systems. 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. The product penetrates the weak/friable surface, filling voids and static cracks and binding loose particles to strengthen the screed. Stopgap SRS acts rapidly, meaning weak screeds can be reinforced overnight to provide a base suitable for the installation of subsequent subfloor preparation products.
Just as when installing floorcoverings anywhere else, flooring contractors need to be aware of the problems posed by damp when applying a surface reinforcement system. Excess levels of subfloor moisture can result in moisture rising up and attacking adhesives and floorcoverings, possibly causing complete floor failure. 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 supress excess subfloor moisture levels. Stopgap SRS can be used over certain screeds containing high levels of construction moisture prior to the application of a waterproof surface membrane.
Contractors should follow individual manufacturer’s instructions when using surface reinforcement systems, and an assessment should be made to determine the condition of the screed, and, therefore, the likelihood of success, prior to installation. In Situ Crushing Resistance (ISCR) tests, using a BRE screed tester to BS 8204, are typically used for these purposes. These involve dropping weights onto the subfloor from specified heights to test the soundness of the screed.
36 | SUBFLOOR PREPARATION
OTHER CONSIDERATIONS Upon removing floorcoverings as part of a refurbishment, contractors may also find that the subfloor is cracked or mechanically damaged. This also needs to be addressed before proceeding to the next stages of subfloor preparation. Where subfloors are very badly damaged, mechanical repair of the subfloor may be necessary. Static cracks as deep as 50mm can be filled with a repair compound, such as F. Ball’s Stopgap 400 repair.
Subfloors where refurbishments are taking place may also be contaminated with oil, grease or other chemicals. Old adhesive residues, such as bitumen and carpet tile tackifiers, may also be present after removing old floorcoverings. In both cases, mechanical preparation of the surface will typically be necessary before applying other floor preparation products. The screed may need to be completely replaced if the subfloor is very badly contaminated.
Recent innovations have resulted in a new time-saving solution for preparing subfloors where old adhesive residues are present. As long as adhesive residues are minimal and well bonded, contractors can apply a levelling compound that’s been specially formulated for use over old adhesive residues, such as F. Ball’s Stopgap 1200 Pro. In such cases, there’s no need to prime before applying, saving further time.
Where subfloors are contaminated and cannot be prepared by traditional methods, F. Ball’s Stopgap Isolator membrane offers a solution. Stopgap Isolator Membrane is 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.
www.f-ball.com/en
www.tomorrowscontractfloors.co.uk
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