Using a real-life example of advice provided by F Ball’s technical service team on the
best course of action for a particular flooring project, Chris McQuade provides a solution for dealing with the relatively uncommon problem of lignite.
WHEN undertaking any flooring installation, it’s important to ensure the subfloor is free of contaminants that may interfere with the adhesion of subsequently applied subfloor preparation products and floorcoverings. While mechanical methods, such as planing or grinding, are effective at removing most surface contaminants, other types of contamination may require additional preparations.
This is the case with lignite, a soft, low grade of coal, which is naturally present in some aggregate sources. Although historically it’s uncommon to find, it’s becoming more common because of the prevalence of pump-applied screeds and its relatively buoyancy, and it needs to be dealt with where found. However, the particle size and typical extensiveness where present mean that it cannot be mechanically removed.
While undertaking a site visit to advise on subfloor preparation prior to the installation of luxury vinyl tiles (LVTs) in the ground-floor kitchens, utility rooms and WCs of several newly built semi-detached properties, each with an approximate area of 80sq m, one of F Ball’s technical service representatives noted that the sand/cement screed was contaminated.
Apart from splatters of paint and plaster, there were speckles of black contamination throughout. There were also several cracks in the screeds in each plot.
Uncommon issue
The technical representative suspected that the black material was lignite. A sample returned from site that was tested, by seeing if it could be used to mark a piece of paper, confirmed this.
A routine moisture test also indicated that subfloor Relative Humidity (RH) levels in the utility rooms of two of the properties were around the limit for installing resilient floorcoverings without a moisture management solution in place, with one giving a reading of 74% and the other 80%. BS 8203, Code of practice for installation of resilient floorcoverings, stipulates that subfloor moisture levels must be lower than 75% RH in these situations.
A particular problem with lignite is that it’s sensitive to moisture – particles that absorb water can expand and protrude from the subfloor, so the installation could not proceed as normal. Neither could we recommend applying a waterproof surface membrane while the screed was still damp. However, once the screed had dried sufficiently, a waterproof surface membrane could be applied to isolate the lignite from the moisture in any subsequently applied floor levelling compounds.
Initial steps
It would first be necessary to allow the screed to dry naturally to a point where a moisture test indicated that subfloor RH levels were below 75%. The contractor would then need to mechanically remove paint and other contaminants from the sand/cement screeds before vacuuming to leave a clean, dust-free, micro-textured surface.
Cracks in the concrete would also need to be vacuumed to remove any dust and debris before being repaired using a suitable repair compound, such as F Ball’s Stopgap 400 Repair, providing that they were static.
It was recommended to wet the floor beforehand to achieve the effect of priming – preventing moisture being drawn from the repair compound and inhibiting strength build up.
A single coat of Stopgap F77 waterproof surface membrane could then be applied to create a barrier between the lignite and moisture in subsequently applied subfloor preparation products. It should be applied using a 1.5mm x 5mm v-notched trowel, before rolling with a pre-coated roller to achieve a continuous pinhole-free finish.
It was recommended that, once the waterproof surface membrane had cured, the surface was primed using F Ball’s Styccobond P141 primer. It is specially designed to promote the application characteristics of levelling compounds when applied to non-absorbent surfaces, including waterproof surface membranes. When the primer was dry, contractors could apply a minimum 3mm thickness of Stopgap 1200 Pro levelling compound and allow it to dry to create a perfectly smooth base for floorcoverings.
Adhesive recommendation
Finally, we advised that LVTs were installed according to the manufacturer’s instructions using F. Ball’s Styccobond F49 Hybrid PS temperature tolerant pressure sensitive adhesive, providing this is listed as compatible in our Recommended Adhesives Guide (RAG).
The use of a high temperature grade adhesive was specified because of the potential for large patio doors in the kitchens to cause solar gain. High temperatures or extreme temperature fluctuations as a result of solar gain can cause floorcoverings to expand and contract significantly, which may lead to unsightly tenting in floorcoverings and gapping at the edges of LVTs over time.
Styccobond F49 is a solvent-free, water-based adhesive that develops the ultra-high bond strength to hold floorcoverings firmly in place when exposed to temperature fluctuations from -20deg C up to 60deg C. Its pressure sensitive characteristics would also help with the positioning and alignment of LVTs.
The good news was that the contamination issues were resolved and works could commence again within 48 hours thanks to the advice provided.
www.f-ball.co.uk
Chris McQuade is a member of F Ball’s technical service team
