UNDERFLOOR HEATING THE HOT TOPIC IN TILING
David Wilson, UK Technical Services Manager at Building Adhesives Ltd (BAL), advises on choosing products for tiling over underfloor heating. We also take a look at BAL’s products in action at a spa.
Ensuring that the correct products are selected for fixing in tiling projects where underfloor heating is involved is essential. This is because heated floors create pronounced fluctuations in temperature, creating movement stresses in the installation during the heating and cooling cycles.
It is important, therefore, that the coefficient of thermal expansion of the rigid tiled finish does not vary too much from the heated subfloor. This is because small changes in expansion and contraction exert greater stresses on rigid tile finishes. In addition, in order to reduce the risks of tiles cracking or de-bonding, adequate preparation and, where applicable, commissioning of the floor heating system is crucial; as is the correct selection of adhesive and grout.
When installing tiles over a hot water pipe system, it is essential that the screed is fully dried. In the case of reinforced cement:sand-based screeds, this can range from six days with a product such as BAL Quickset Cement, to a minimum of three weeks for a screed containing Ordinary Portland Cement (OPC), before commission of the underfloor heating.
For calcium sulphate screeds, whether anhydrite or alpha hemihydrate screeds, surface preparation and drying time is particularly important. The drying time is dependent upon the thickness of screed and could be extended further, dependent upon site conditions.
Following this period of curing, the screed may be commissioned by heated slowly at a maximum rate of 5°C per day up to the maximum operating temperature as recommended by the heating manufacturer. The temperature of the screed should be maintained at this level for a minimum of three days, before allowing it to cool to room temperature.
Ensure that the heating system has been turned off, or on in cold
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temperatures, to ensure the screed is at 15°C before tiling commences. Before tiling, the surface should be scarified to remove any laitance which can form a barrier to adhesion.
“WHEN INSTALLING TILES OVER A HOT
WATER PIPE SYSTEM, IT IS ESSENTIAL THAT THE SCREED IS FULLY DRIED.”
When using cable systems, check with the manufacturer to ensure the system is compatible with the intended substrate and application areas i.e. kitchen, bathroom etc. The cables should be bedded into a layer of self-smoothing compound, such as BAL Level Max. Developed with innovative Fibre Strand Technology (FST), BAL Level Max can be used for bed depths up to 80mm thick.
When using an uncoupling system, such as BAL Rapid Mat, the heating cables should be below the membrane and encased within the levelling compound. Before tiling, the surface of the mat should be primed using a contact adhesive, prior to the installation of tiles using the correct adhesive.
When tiling onto concrete or cement: sand screeds or plywood overlaid floors (min thickness 15mm), a suitable flexible tile adhesive is required such as BAL Single Part Flexible, BAL Rapidset Flexible Fibre, or BAL Max Flex Fibre.
As with your adhesive choice, your chosen grout should also be flexible to allow for thermal movement.
Due to the large number of heating system on the market, we would also recommend to contact BAL Technical Advisory Service (TAS) for advice before any work is carried out!
Turn to the next page to see BAL’s products in action.
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