This month, Steve Spinks provides advice on installing floorcoverings in old buildings.
Floorcovering installations in old buildings, particularly those built more than 50 years ago, frequently turn out to be more complex than initially expected – you don’t know what you’re going to uncover when you remove old floorcoverings.
Amongst the concerns that may be faced by contractors when refurbishing floors in old buildings are the presence of adhesive residues and contaminated, damaged or cracked subfloors. You also frequently have to deal with a multitude of different substrates. There’s also the familiar problem of damp, which very old buildings are more prone to because they will be less likely to incorporate a structural damp proof course.
This was certainly the case when we were called to offer advice on the refurbishment of an old school building in central London.
Initial inspection
The areas being refurbished were ground floor classrooms, corridors and WCs. Several classrooms had new screeds, installed as part of the refurbishment. There was a classroom with timber floorboards. In another one, carpet had been removed to reveal a relatively new screed, installed as part of previous works. Old adhesive residues and a previously installed levelling compound were left behind.
Ceramic tiles had been removed from the toilets, leaving old ceramic tile adhesives, and there was a section that had been dug out and filled with a new sand-cement screed.
In the corridors, there was asphalt. Over this there was a red coating (possibly a waterproof surface membrane) and the remains of a levelling compound, as well as old adhesive residues. The asphalt appeared to be sound, apart from at the edges where walls have been removed as part of refurbishment. Channels had been cut through the asphalt, which had been filled as part of the refurbishment and earlier works.
The issues
Despite the sections of new screed having structural damp-poof membranes in place, a moisture test indicated that residual construction moisture was too high to install floorcoverings directly over these subfloors without the application of a moisture management solution. 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 rising damp is often more likely to be a concern in buildings built before this time. The building is of such an age that it is unlikely to have a structural damp-proof course throughout, so in all areas without adequate protection from rising damp, a moisture management solution, such as a liquid waterproof surface membrane, would be required.
The impervious nature of asphalt means that, if sound and uncracked, it will provide a barrier preventing moisture reaching the level of floorcoverings. However, the application of a waterproof surface membrane will be required where there are infills.
Recommendations
Based on these observations, we were able to recommend the following course of action for the flooring contractors to take:
It would first be necessary to clean off all surface debris and other trade waste from the subfloors. All adhesive residues and old levelling compounds should also be removed by mechanical means to leave a clean base.
If the asphalt is not in a good condition, that too would require removal by mechanical means. Otherwise, the surface should be abraded to remove adhesive residues and the pre-existing levelling compound. Any loose ceramic tile adhesives in the WCs must also be removed, ensuring what remains is sound and well bonded. The floorboards should be overboarded with flooring grade plywood, fixed at 100mm intervals (see BS 8203:2017 for details). The joints between panels and indents formed by screws can then be filled using an appropriate floor finishing compound, such as F. Ball’s Stopgap 500 Micro, to ensure a perfectly smooth base for other subfloor preparation products.
Contractors may then proceed to apply F. Ball’s Stopgap F77 two-component waterproof surface membrane in areas where there are no barriers against residual construction moisture or rising damp, except the classroom with timber subfloors. The product will isolate excess subfloor moisture where RH values are up to 98%. Where it is applied to infill areas in the corridors, it should overlap the clean asphalt surface by at least one metre to provide a continuous barrier to the passage of moisture.
After that, contractors should prime all areas using Stopgap P141, F. Ball’s primer for non-absorbent surfaces, including waterproof surface membranes, before applying F. Ball’s Stopgap 1200 Pro. The levelling compound can be applied over old adhesive residues, including ceramic tile adhesives, meaning one product can be used for the whole project.
Potential solutions required
If the subfloor is still rough or uneven after the initial subfloor preparation, including mechanical removal of old adhesives and levelling compounds, contractors may wish to apply a layer of F. Ball’s Stopgap 1200 Pro levelling compound to improve the coverage rates of the subsequently applied waterproof surface membrane.
Also, if the removal of the asphalt is required, F. Ball’s Stopgap 600 Base may be applied up to a maximum thickness of 50mm to bring the floors up to the same level prior to smoothing the entire area.
Final steps
Once the levelling compound has cured, contractors can proceed with the installation of resilient and textile floorcoverings using compatible flooring adhesives. To check the compatibility of F. Ball adhesives and chosen floorcoverings, flooring professionals can consult F. Ball’s Recommended Adhesives Guide or the floorcovering manufacturer’s guidelines.
Steve Spinks is F. Ball technical representative for The East.
F. Ball’s regional technical representatives provide advice to flooring contractors on how to get the most out of F. Ball products, including conducting site visits and producing case-specific reports advising on the best course of action for particular flooring projects. Find out who your technical representative is here.