Technical Note: cts 4a

Floor Tiling with Underground Heating

Reference to BS 5385 part 4, section 10.3.5.2. British Standards recommend the following:

“Floors with underfloor heating generally operate below 30 degrees centigrade. The heating elements are usually incorporated in a suitable reinforced mortar screed with a minimum thickness of 75mm.
Expansion Joints (movement control joints) should be incorporated at the perimeters of the screed, and also around all upstands or anything which penetrates the screed. These joints are usually formed whilst the screed is being laid, by installing preformed 10mm thick strips of expanded polystyrene against the wall or upstand. It is essential that movement control joints penetrate the full depth of the screed. The screed should be cured and allowed to dry out normally for a minimum of 3 weeks, after which the floor should be brought to the intended surface temperature and maintained at this temperature for a minimum of 3 days, then allowed to cool to room temperature before tile fixing commences. Movement control joints should be incorporated at all perimeters and upstands, to coincide with those in the reinforced base screed.”

When tiling over heated or flexible substrates reference should be made to BS 5385-2:1991 which recommends that movement joints be placed at 6m intervals in both directions. The movement joint width should be at least 6mm.

Allow 28 days after completion before initially bringing the floor back up to its operating temperature at increments of ≤ 5 degrees centigrade per day.

Failure to follow these guidelines when installing tiles on heated backgrounds will result in the finished floor cracking and/or tiles debonding from the substrate.