Bathroom floor for tiling

[llama]

Realise there's a lot of posts on this but wanted to be sure before doing something I may regret.

I'm going to tile the bathroom floor. The existing floorboards have mostly been removed for plumbing, electric etc and they're pretty knackered so I intend to replace with ply. The joists are 400mm centres approx and whilst the room is 2300x1600 the tiled area is only about 1600x1600mm.

I don't want to build the floor height up too high so was considering one of the following options. Not sure which is best and was hoping for some advice.

Tiles on a 6mm hardie backer on 18mm plywood EN636-2S.
or
Tiles straight on top of 24mm or 25mm plywood EN636-2S.

Appreciate your thoughts.

 

[Gerrydelasel]

How big are the tiles? (Big tiles are less tolerant of defects)

 

[llama]

Ceramic 200mm square. Can't remember if they're 6 or 8mm thick.

 

[Paul C.]

Personally, I think there are too many variables with ply, I'd rather be going down the 18mm Ply and Hardie route. Ply on its own regardless of thickness needs to be screwed at 300mm max in each direction, which you can't do with your 400 joists with out placing extra noggins before the ply goes down.