Bathroom floor in new build on Chipboard?

[thegwads]

hi
starting job on monday. a new extension on a pretty large house. Anyway, development company wants me to tile the bathroom floor, upstairs. Already laid with 25mm chipboard, and i do not think it is the green shiny stuff.
I recently did a repair job on a new build house which had tiles laid directly on to the chipboard staright away, and allowed no time for the house to settle. As a result, massive cracks along the tiles on the chipboard join, where the movement of the chipboard boards occured.
So, i have stated my reservations about tiling on to chipboard, and indeed to tile any new build. Have recommended waiting a year for settling, then tile. Also, not possible to 18mm ply as the floor levels will be out and not acceptable. The development company are cool, and if i am not happy, do not do it. Also, the workmanship is of the highest quality i have ever seen. There is no movement at all on the chipboard. I do however want to fully cover myself. So will no more ply, ditra matting, or hardibacker be a suitable thing to use.
I want to use ditra, as no screwing involved ( I think), will this be fine to use?
Any suggestions how tyo tackle this would be massively appreciated! i.e. what addy to use, the exact process, with priming etc???????

cheers

 

[CJ]

6mm hardibacker.

 

[thegwads]

does that require screwing and addy?
cheers

 

[CJ]

Yes..........but only 20mm screws..so not to go right through Chippy floor

 

[thegwads]

done that before!!!!!

 

[thegwads]

and i take it just usual spf addy? and flexi grout?

 

[grumpygrouter]

if you are positive tha the floor is solid, i would be inclined to use ditra or durabase. At least then you ahve a bit of security against lateral movement. Won't help against flexing though.