Tiling down stairs toilet floor

[i_am_fubar]

I have a small downstairs toilet that I'm redecorating, and wish to tile the floor of it. The floor isn't very stable, and I think some of the boards are rotting.

I plan to replace any bad floor boards and joists. However, I don't want to run the Risk of the floor cracking through movement. Therefore, is it acceptable to fit a 12mm sheet of marine grade plywood over the entire floor for extra stability? I'm aware that it will leave a small step from the other floor covering, But I am prepared for that.

Cheers,
Sam

 

[Symptoms]

fubar - if possible (do try, as it'll make the job easier) take the bog pan out first. Remove ALL the floorboards (bin them), repair the structural timbers below, re-floor the whole area with a single piece of 18mm of exterior grade ply. Then tile the whole area, then refit the bog. Double check heights/distances of water & soil pipes 'cos you may need a couple of extra fitting when putting the bog back.

 

[i_am_fubar]

Not a problem there. I'm going to be ripping the guts out the room, plasterboard off, re-inforce wall joists and straighten. May need to look at putting additional supports between the foundation and joists.

Gotta re-plumb the sink up and through the wall. Re-drill overflow and filler pipe holes. The list goes on.

Still, if its ok to use solid board for the floor. I shall be using that

Cheers,
Sam.

 

[Symptoms]

Sam - the point about using thick EXTERIOR ply is that it's a perfect, stable base for your floor tiles. Advantage of getting it down as a single piece means there are no joins to flex, thus cracking the tiles above. If you have to join the ply ensure these are above joists for support (no flexing) or introduce noggins for this support. Screw the ply onto the joists and make sure all the new structural timber is treated. Use flexible floor tile adhesive, stuff designed for wooden floor to tiles.

 

[i_am_fubar]

Hmmm, if I'm going to treat the new noggins, would it be worth treating the ply too, or is that just pointless considering that it's exterior grade? Just want to maximize the life span of.... well... everything.

 

[vv2806]

Check the sticky at the tiling forum. Very useful. Also some of the pros there said he would ude 25mm ply if there is nothing underneat and 18 mm ply on top of existing floorboards.