Before tiling into anything there are 4 boxes that need ticking for the substrate..Can tiles be lifted (and underfloor heating) or would we be mad to go down that route now?
1. Surface should be dry
2. Surface should be clean
3. Surface needs to be structurally sound
4. Surface needs to be flat
If any one of these is not ticked off then no tiling should be done.. and no manufacturer will guarantee their products if they Aren’t
your tiler should have ensured the floor was flat, dry, sound and clean before he started..
He should be putting this right out of his own pocket