Wet UFH on Block & Beam and Joists... - TilersForums.com

[Chalker]

50-55 is minimum for tiling onto. Speak to a screed supplier, they can add fibres to strengthen it. Then it can be reduced by a bit.
@Ajax123 on here is the forum expert on here.

 

[Dumbo]

Calcium sulphate screeds can go in thinner than sand cement screeds .

 

[Swindiff]

Gyvlon Thermio+ can go down unbonded onto insulation at a thickness as low as 35mm. I had it installed in my kitchen on top of 50mm celotex. My minimum thickness was 36mm, maximum was 52mm and average was 48mm. More than pleased with it and extremely responsive to the heat in the UFH pipes. I can start to feel it coming through the floor in less than 30 minutes with porcelain tiles laid on top. I had heard all the stores of UFH having to be run pretty much constantly because it takes forever to heat up and cool down, not with this stuff, my UFH gets turned on and of as I would have with the radiators.

Gyvlon Launches New Thermio+ Screed; EasyFlow to Supply Nationwide | EasyFlow - http://www.easyflow.org.uk/news/thermio-screed/