tiling over floor half screed/half chipboard

[jonnyc]

just been to see a floor that will be tiled in 15 mm limestone when kitchen knocked through and extended.
approx 20,.00 sq mts 30mm tongue grooved chipboard laid on insulation.
15.00 sq mts existing screed butted up to chipboard.
another 15.00 sq mts of new screed to go down up to old screed and chipboard.
i will be laying electric heat mats.
i am going to suggest 12mm dukkaboard over whole area.,
Am wondering if i should suggest chipboard removed completely and then new screed laid up to old before boards go down or could leave chipboard in place and screw dukkaboard down on to chipboard as well as stick.

 

[Rookery]

So 20 mtrs chipboard is a floating floor? That + UFH + limestone = recipe for disaster. I'd have that taken up and the area screeded. Once the whole floor is solid, I'd Ditra it before tiling, not forgetting perimeter and intermediate movement joints.

 

[swanman]

as above