Browning as a substrate for tiles?

[mscg]

well thats that option gone then!

 

[Droopy]

I could well do as there is a fair depth to make up in places - what board could you recommed given its got to hold 400 x 400 travertine? - I would have to dot an dab the boards

If it is a Bathroom/Shower room, the dry areas should still be moisture resistant 12.5mm (Green board). This could also be used in the wet areas, but MUST be tanked. BAL WP1 would do the job.
Or the wet areas could be lined with a Tile backer board, such as Wedi.

If it is a Wetroom, the tanking should be extended to the "dry" areas to a height of 1m. And ofcourse the entire floor should be tanked too.

 

[Spirit]

Without knowing the surface and thickness you are trying to achieve, it is hard to give an exact answer, but assuming that the surface is solid and reasonably flat, I would dot & dab a tile backer board, with securing screws inserted the following day for extra security. If the surface is a poor, scratch up with sand/cement render first. The render will be dry enough to fix the boards after two days.