A SOUND BASE
F. Ball Technical Service Manager Stephen Boulton gives his tips on how to deal with contaminated subfloors, including the latest, non-mechanical methods available.
Contractors assessing the condition of a subfloor prior to installing floorcoverings will sometimes find it contaminated by oil, other chemicals or old adhesive residues. Any contamination needs to be dealt with appropriately to prevent potential floor failure unless the entire subfloor is to be removed and replaced.
Applying a levelling compound to a subfloor is the usual step to creating a suitably smooth base for the receipt of new floorcoverings, helping to ensure a visually attractive finish. However, before doing this, contractors need to make sure that the substrate is suitably sound, smooth, dry and free of contaminants before proceeding.
Where contaminants are present, such as oil, grease, paint or other chemicals, remedial action will be required before a levelling compound is applied. This will ensure proper adhesion of the compound to the substrate, avoiding the potential for de-bonding to occur, which could cause complete floor failure.
TESTING Where surfaces are contaminated, the depth and type of contamination should be checked to determine if it is possible to prepare a surface for overlaying; oil can penetrate many centimetres into concrete, and although the surface may be cleaned, contaminates can migrate back to the surface.
Contractors should refer to British Standard (BS) 8204, covering best practice for concrete bases to receive in-situ floorings, for guidance. Recommended tests include taking cores from the most contaminated areas to gauge the depth of contamination and adhesion tests, looking for a tensile pull-off strength of at least 1.5 N/mm2
.
Where contamination has penetrated the surface of the substrate, it will not be possible to simply remove it by cleaning; mechanical preparation will be required. Methods for doing this include dust-free shot/grit blasting and mechanical planing, scabbling, grinding or abrading. Hand tools may also be used for edges and hard to reach areas.
ALTERNATIVE SOLUTIONS Where mechanical surface preparation will not be sufficient to
18 | TIP OF THE MONTH
properly remove the source of contamination, there is another alternative to completely removing and replacing the subfloor.
In situations where a fully bonded system is not required, instead of using a levelling compound to prepare the subfloor prior to the installation of floorcoverings, contractors may use an isolator membrane, such as F. Ball’s Stopgap Isolator Membrane. Stopgap Isolator Membrane is an impervious loose lay sheet that can be laid over the contaminated subfloor, creating a barrier between the subfloor and floorcovering. New resilient floorcoverings are then adhered directly to the isolator membrane.
ADHESIVE RESIDUES In some cases, contamination of the subfloor may be in the form of adhesive residues left behind when old floorcoverings were removed.
Traditionally, contractors would have had to remove old adhesive residues with the same mechanical means used for dealing with other types of subfloor contamination. Now, levelling compounds are available that can be applied directly over old adhesive residues, providing a timesaving solution to the problem. These include F. Ball’s Stopgap 1200 Pro, which can be applied directly over minimal, well-bonded adhesive residues without the need for priming to save further time.
FINAL CHECKS Once contamination has been dealt with, contractors should, once again, assess the condition of the subfloor before proceeding with the installation. This involves checking the subfloor is suitably sound, smooth and dry. Dust or debris should be removed, and damaged subfloors should be repaired with an appropriate repair compound.
Where an isolator membrane is not being used to overcome subfloor contamination, a moisture test should be conducted to check the surface is dry enough to receive floorcoverings. Where subfloor relative humidity levels are above 75% (65% if wood floorcoverings will be installed), a waterproof surface membrane should be applied to prevent excess subfloor causing floor failure.
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