Plyboard floor advice

[blackadder]

Ripped up old floorboards and going to put down 18mm ply then 6mm hardibacker to tile onto or similar, does the ply have to be wbp or can I use cheaper ply as it will have backer board on top.
Thanks

 

[mike1979]

What about using 18mm weyroc could get away with using uncoupling membrane on it then

 

[blackadder]

What about using 18mm weyroc could get away with using uncoupling membrane on it then

Thanks for your reply, didn't want to use chipboard thought I might be able to save by using a cheaper ply as the backer board should stop water penetrating.
What do other tillers use.

 

[White Room]

Backer board is water resistant not waterproof....