Suspended floor with wet UFH query.

[Rookery]

Been to see a job tonight, 2 1st floor bathrooms tiled by a builder in a barn conversion. Needless to say its a poor job and they want them re-doing properly. They've already had a 'tiler' in (off one of them ratings sites) to repair cracked grout and of course its cracking again. It looks like the floor tiles are fixed direct to a timber floor finish and somewhere underneath is wet ufh. I've only ever experienced tiling over wet ufh in a screed. What is the likely make-up of this sub-floor?

 

[White Room]

You say suspended, is that joists....

 

[Ajax123]

Could be diffuser plates under the floor boards. Not a fantastic system to tile on to. They would be better removing the floor boards, making sure the pipes are properly supported then screed between the joists.

 

[Rookery]

Its hard to tell but by tapping the tiled floors and judging by the bounce it seems like a suspended timber floor. Also the ffl of the adjacent carpeted bedroom & landing is very similar, leading me to think its tiled direct to wood. It definitely does not seem to be a block and beam floor. As Alan suggests, I'm half expecting some sort of plates under the floor. I'd normally overboard any timber floor with Hardie (or Marmox if elec ufh) so if I were to do this here, am I reducing the heating effect? Would the Hardie act as a barrier and actually cause an unwanted build up of heat underneath?