Tiling bathroom floor

[Dougie]

In the process of renewing my bathroom and looking for advice on flooring for tiling.

Bathroom has a suspended timber floor with 25mm tongue and groove floorboards. Cant remove the floorboards or else I'll be pulling down 2 stud walls so not really an option to remove & replace.

The floorboards are pretty straight and solid with some cut outs here and there from the old layout which I have patched up.
Question is whats best to overlay the flooring with before tiling?

Was thinking either:

• 9mm ply
• 3mm hardboard topped with 6mm cement board
• cement board direct to floorboards

 

[One Day]

How big is the area?
No to 9mm ply.
No to 3mm hardboard - anywhere, anytime, any situation.
Hardibacker 6mm bedded in adhesive and screwed will give a sound surface for tiling.
My preference would be 10mm Wedi though, as it's waterproof.

 

[Dougie]

Bathroom is about 1800x2500