For solid floor construction, a
normal sand/cement floor screed can be used. No special
additives in the screed are required. Where the pipe is laid on
insulation, the minimum screed depth
must be 65mm for domestic applications and 75mm for commercial
applications as specified in British Standards.
The optimum screed thickness is 75mm
but no more than 90mm, for most applications. Where heavier
floor loadings are required, the construction engineer should
advise on the screed thickness.
Specialist Anhydrite (Calcium
Sulphate) Screeds, when used with underfloor heating, must
provide a minimum 30mm coverage over a pipe or conduit. Careful
consideration must be given to the expansion of heated screed
floors. As a guide when using semi-dry cement and sand screeds,
BS EN1264 - Part 4 recommends a maximum screed area of 40m2 can
be laid without expansion allowances. With Anhydrite screeds
much greater areas can be laid without expansion joints; e.g. in
Sports Halls up to 600m2.
When using an Anhydrite screed
always check with the supplier for their requirements. The
screed must be allowed to dry and cure normally, in accordance
with the relevant BS Standards and manufacturer and supplier
instructions, before initial heating and system start-up. The
underfloor heating MUST NOT be used to speed up the curing
process.
