Floor preparation for large format porcelain tiles

[ir50]

Just doing a bathroom reburb. The floor is to be tiled in 600x600x10mm porcelain tiles. Bathroom size approx 2.5mx2.5m.
As I had to lift a lot of the floorboards for the new pipework, I decided to replace the lot with 18mm WBP ply. The plan then was to use Ditra and then tile. I'm just a little concerned if the 18mm ply is strong enough for the heavy tiles.

1. Should I re-enforce with another layer of say 12mm or maybe a backerboard?
2. Is the Ditra matting necessary?

Thanks in advance

 

[Gazzer]

The Ditra will do nothing if the floor is not strong enough.
I would strengthen the joists and screw the ply every 200-300mm. It should be strong enough then but I always overlay with 6mm backer boards for a good surface to tile to.

 

[ir50]

What are you meaning by strengthening the joists? They are 200x50mm spaced about 300mm apart?

Any recommendations on backerboard to use...no more ply, Hardie?

When would you use Ditra rather than backerboards?

 

[Gazzer]

Seeing as I cant see or feel if yo have any movement on the floor it will be up to you to decide if its strong enough but rather than piling on more ply it is always better to beef up the joists before hand and cut down on any height issues it would create.

Ditra is mainly for lateral movement and problem substrates etc.