SURFACE PREPARATION GET THE RI David Wilson, UK Technical Services Manager at Building Adhesives L
Before floor tiling begins, it is critical that subfloors are prepared properly. This means that they must be level, sound, dry, free from deflection, dust and any other contaminants which may be considered barriers to adhesion.
It is important that any new structural concrete should be left to cure and dried in air for at least six weeks. Cure cement:sand screeds for a least seven days, before drying in air for a further two weeks. A longer period of time will be required in poorer drying conditions and or when heating the floor.
As a general rule of thumb, the drying time for a Calcium Sulfate screed, so the moisture content reaches 0.5% w/w, is approximately 1mm per day up to 40mm in ideal drying conditions – i.e. air temperature of 20C with a relative humidity not greater than 65%. Drying times will significantly increase for thicker screeds or those in poor drying conditions.
Accelerated drying of Calcium Sulfate screeds may be used once the screed is at least seven days old.
Ensure that any direct-to-earth subfloors incorporate an effective damp proof membrane – such as BAL DPM – a
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one-coat liquid applied system that can also be used as a primer and waterproofer.
If you are laying tiles or slabs directly to the floor using tile adhesive, the maximum permitted deviation underneath a 2m straight edge resting on the floor should be 3mm (SR1).
A suitable smoothing and levelling floor compound - such as BAL Level Max - can correct surface irregularities and, therefore achieve SR1 on new and existing floors. Available in one-part or two-part forms, they are easily mixed and simple to apply, they find their own level giving a smooth finish for laying tiles or other floorcoverings.
There are a number of products on the market, each with different features, generally going from anything from 2mm up to 80mm in bed depth.
BAL Level Max is one of the only levellers that can go up to 80mm bed depth in one application. It can also be tiled on in only four hours – at any depth – meaning fast-track tiling is possible.
In general, smoothing and levelling compounds are not designed to be used as a finished, or wearing
www.tomorrowstileandstone.co.uk
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