I've already installed plywood to wet-room walls - do I need to remove/replace?? - Tile Advice

[ojtiler]

I would appreciate advice for my project for my wet-room project. Having already received some helpful guidance on edging strip in a separate thread, I've also realised by reading many other posts that plywood is no longer a recommended substrate for the walls in this application - and there may be additional work needed for the ply floor, too!.:mad2:

Here's what I've done already;
The room is approx. 2mx2m square. Two of the walls are stud work and I have already screwed 12mm WBP ply to these (the other 2 walls are newly plastered). The floor is new 22m WBP ply (same thickness as the Impey Linear shower tray I bought). The floor is in 2 panels each ~1mx2m screwed down roughly every 120mm onto doubled joists, with the join along the centre line of one of the joists. I had to 'sister' the joists to get the floor level and there is no detectable movement on the floor.

Here's what I was originally planning to do, based on advice from the suppliers;
- coat 12mm ply walls in BAL WP1 waterproofing compound, polyester tape to the wall gaps
- tank the floor with Impey supplied membrane
- bond tiles to wall and floor with Larsen flexible standard adhesive.
[Tile + adhesive weight loading will be about 25kg/sqm (within the range Larsen recommend for the adhesive)]
- grout with waterproof BAL Easypoxy grout to completely eliminate water transfer through the joints

An obvious solution (involving a lot of work + more cost) would be to completely remove the plywood and replace with e.g. Marmox board, then proceed with the tiling as planned. So, questions I have are:

1. Is this necessary, based on your experience, or is my original plan going to be robust enough?
2. Would an acceptable compromise be to over-board the ply with thinner Marmox panel (e.g. 4mm, or 6mm?), then tile?
3. Impey have advised no over-boarding needed on the floor (just membrane straight onto ply); are they right?
4. If I install Marmox boards, would they need priming before tiling?
5. I have read tile boards containing silica can cause silicosis.... do Marmox contain Silica?

Sorry so many questions for only my second OP, but I would really appreciate your help working out which way to go!


Many thanks.

 

[Perseverance]

Re: I've already installed plywood to wet-room walls - do I need to re

What did you do in the end? I am trying to sort out somebody else's bridge job and find myself with the same dilemmas.

I am trying to re-tile one wall of my shower cubicle. Already purchased replacement plywood before discovering it wasn't ideal, due to heat expansion. Bal said it would be fine to use if I painted back & sides with SBR and used their tanking kit.

Was going to use their grout and add their GT1 Admix to give extra flexibility
because of the wood, but since learning that epoxy grout is the only true waterproof grout I thought maybe I should use this and forget the tanking? The other wall of the cubicle was also letting water through however the tiles are stuck too firmly to remove, so I can only replace the grout on that side

Can anyone tell me if Easypoxy will be suitably flexible? The Bal person said it did contain polymers but I would really appreciate some experienced feedback.

There also seems to be a lot of conflicting advice around on tanking. Some, including Bal, say you should always tank regardless (possibly because their kits retail at over £70 a pop!). However others say tanking is not necessary when you use products such as Aquapanel, yet Aquapanel, like all non-epoxy grout, is apparently only water resistant rather than water proof. Am I missing something here? If you are going to tank then why not just use plasterboard, as the water is never going to reach it anyway?

Please forgive if these seem like stupid questions - new to all this!
Many thanks,
Confused newbie

 

[Qwerty]

Re: I've already installed plywood to wet-room walls - do I need to re

Use plasterboard if tanking with a membrane or paint on type tanking product...... fit Marmox or similar (100% waterproof) as an alternative