Preparation adhesive and leveling - Tile Advice

[bruggsy]

hi
im in the process of floor prep for ufh. the floor is out by up to in 15mm in places and wondered if i could level up with tile backer boards on deep bed tile adhesive?
if so which tile adhesive would be best?

 

[Dave]

Concrete or timber floor. ?

 

[bruggsy]

Concrete or timber floor. ?

Concrete floor

 

[Dave]

Concrete floor

Bed the insulation boards down, install ufh and then levelling.