Marine ply please help

[richardkear]

Totally confused now. Have recently pulled up tongue and groove flooring and replaced with 18mm marine ply to tile directly onto.
I also have one wall that I intend to tile on which will be 12mm marine ply. I have used this as I have to fix a concealed mixer riser rail and several other fitting to it. I also have a recessed shelf in this wall.
I posted a question ref tiling a window header which I boarded out in 12mm marine and asked why it was ply and could it be plasterboard.
Questions
1. Is the 18mm marine ply floor ok to tile onto
2. Do I now have to overboard the 12mm marine ply with plasterboard
3. Same question for the window header.
The marine ply wasn't cheap but I read elsewhere this was the way to go

[whitebeam]

What tiles are you fixing.

[doug boardley]

I don't condone tiling direct onto ply, primed or not.If it's already in-situ I'd be overboarding it with some 6mm hardie, marmox,wedi type board.

[richardkear]

Wall tiles are 450 x 250 x 8mm ceramic (marble look alikeys)
Floor is 450 x 450 x 10 mm ceramic (same as above)
Been advised to use 6mm bed on walls and 10mm on floor

[whitebeam]

As Doug with the 6mm hardie etc.

[Tony321]

Hi Richard,
1)As long as Wooden Floors timber bases must be rigid. Is the marine ply directly over the joists if so i would put knoggings at the edge of the plywood. Seal rear and edges of timber, do not prime the surface, but clean off timber dust.
2)If you choose to tile over plywood you need to Seal rear and edges of timber, do not prime the surface you are tiling on, with an acrilic primer?
Also the plywood should not be butted up leave a 2mm gap for slight movement, also use a cement based flexable adhesive with a solid bed (in shower) it is always best to tank showers with a waterproof kit.

6mm Wedi board on top would be the best option if the buget allows.

But if done correct the ply will be fine.

[diamondtiling]

Priming the ply depends on the adhesive manufacturer used, some say to prime the face and others say not to so you need to check that out.