tiling over chipboard over water underfloor heating.

[jonnyc]

got a couple of bath floors , where water underfloor heat pipes set in metal trays between the joists.
contractor has overboarded with 22 moisture resistent chipboard . tonge/grovved and screwed.
no movement under foot.
I used to lay ditra over chipboard but schluter now say they will not guarantee ditra over timber substrate with water.
trimlime have told me their 6mm cement board xl like hardibacker screwed in to chipboard will be suffice.
is this ok or any other suggestions

 

[Perry]

not sure trimline would know only what the cement board salesman would tell them Jonny mind you i would be prefer to trust a used car salesman lol sounds like a no no from me others may say different :yikes:

 

[Peter]

May be wrong but would the cement board not block the heat too much?

 

[jonnyc]

May be wrong but would the cement board not block the heat too much?

no apparently it lets heat through the board unlike marmox/dukkabaord/wedi or similar.
they say that apart from letting heat through it is a good background to tile on to.
its just 6mm seems very thin but i guess that if chipboard load bearing adn rigid fix , the xl board is just giving a good substrate to fix to.
i have always fixed ditra in the past in this scenario , but now schluter dont recommend

 

[Peter]

Good to know. Ever had any problems using Ditra straight over well screwed chipboard? Never done it myself but would be a more time efficient way than overboarding every time.