Although some tiles, such as quarry tiles, will hold back a great deal of damp, it is not advisable to use tiles as a cure for damp floors.
You can test for damp by placing upturned jam jars on doughnut rings of putty. Leave them overnight and if in the morning there is moisture on the inside of the jars, the floor is damp (1).
If there is rising damp in the floor, it should be treated first. You can use a paint-on solution such as water-based bitumen emulsion. Apply two coats and lightly sprinkle sharp sand on the top coat to give a good key for the tile adhesive.
In most cases, the adhesive used to stick down floor tiles can be laid in a thick bed which will allow for slight discrepancies in the floor surface. If the floor is uneven, it is better to float a screed over the floor. This can be done with a self-levelling screed which is mixed with water in a bucket, poured over the floor and spread with a trowel. Alternatively, for a thicker screed, you can mix up three parts sharp grit sand and one of cement with three parts water to one of PVA. This can be trowled into the low areas and feathered out at the edges.
Where a floor crosses from wood to concrete, as in a kitchen extension, it is almost certain to crack along the division if it is tiled over. To avoid this, you need either a flexible silicone joint at this point, or sheets of 1/2in plywood laid over the wood and concrete as an interlayer. The plywood can be stuck onto the concrete with panel adhesive.
Previous
