Unfortunately I don't know what he has primed it with. Some white liquid is all I know.The latex has been mixed way too wet by the looks of the light colour of it so was bound to fail. What did he prime it with? is he floor solid when you walk on it or is there any deflection in the floor (up and down movement?) If the deflection is minimal, remove the ply and get back to floorboards, make sure the floor boards are screwed down then overboard with 6mm backerboards such as no-more-ply or Hardie. Then either A: lay the electric UFH matting and use self-leveller to cover wires and get floor level for tiling or B. level floor over the 6mm backerboards and use a decoupling matting such as dural that has the groves incorporated to clip in a lose wire UFH circuit and tile directly onto that.
If there is too much deflection in floor then unless you get under the floor and strengthen to alleviate the movement, you will need to avoid using a tile i'm afraid as it is bound to fail regardless.
Hope this helps.
In terms of the floor, I am not sure if there is any deflection however the previous tiler said the floor was solid
I am trying to get some tilers to quote me on the works. I am trying to get quotes for the following:
1. Remove the Latex
2. Check if the Ply is good and screwed in properly. If it is, continue the work again, using the appropriate materials (Insulation boards, UFH, leveller, Ditra)
3. If the ply is not good, to remove it and start again, using cement board, then UFH, Leveller, Ditra.
Is that the correct approach? Seems to me all the responses above do suggest the use of an uncoupling membrane, which I thought was essential, especially when using UFH which causes contraction and expansion.