Ply overboard on top of UFH moving and tiles cracking

Cowboy job , they don't want screwing plywood because easily can be damage ufh pipes. solutions lift up all tiles and whole areas layout with Liquid screed, also known as flow screed, is a self-levelling and ideal for use with underfloor heating as it completely envelops heating pipes, eliminating any voids or air pockets. This results in greater thermal conductivity.

Hi You are correct, its an absolute no no to tile onto ply (as detailed within BS5385-1) let alone onto ply over UFH. Sadly, the only solution is remove the existing tiles and ply and then encapsulate the UFH pipework within a cement based screed or self-levelling compound. Keeping in mind that cement based screed will dry at a rate of 1mm per day for the first 40mm and then 0.5mm per day for the remaining depth. You will need to install a decoupling membrane onto the new screed to ensure the UFH can expand and contract without transferring stress into the tiles above. Schluter Ditra Mat can be installed onto the freshly laid cement based screed just as soon as you can walk on the screed without leaving footprints. Enabling a quicker tile installation without waiting for the cement based screed to fully cure. Schluter Ditra Mat is designed to permit moisture to escape form the screed and dissipate to the edges, ensuring the cement based screed dries at a normal rate. Should you encapsulate with an Anhydrite based product, you will need that to dry and ensure that the Anhydrite screed has a residual moisture content of 0.5% However, with the use of Ditra (ensuring it is installed correctly as full waterproof / decoupling system tiles can be installed with a moisture content of 2% (by volume). I hope this helps. Regards Shaun.