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Hi

Renovating the bathroom in an old house.

Walls and floor are neither true vertically or horizontally.

Levelled the floor and fixed 18mm exterior ply to the walls to be tiled so they are now at right angles to each other and the floor.

Going to use large format tiles 75cm x 25cm.

What should I use to seal the ply and which adhesive is the best out there. Plumber installing the shower suggested I should paint the new wood with PVA but that doesn't fit with previous posts on here.

Any advice welcome.

should have used 12.5 mm plasterboard on walls instead of ply.

Why, and how can you decide and state that without knowing anything about the house, age of house or any other considerations?

Not a lot of point responding to a very easy question with something totally irrelevant.

Assuming that the ply is securely fixed and can take the weight of the tiles then you need a proper primer (NOT PVA) something like this

http://www.tilegiant.co.uk/primer-g-1kg.html

And then use a single part flexible adhesive, I use this

http://www.tilegiant.co.uk/tile-grout-a ... esive.html

But note that it's a rapid set, you may want a standard set depending on your tiling skills.

What walls has the ply been fixed to....brick, stud?

There is quality ply which stands the test of time and also a cheaper 'exterior' ply which is prone to de lamination.

Hopefully you sealed the back of the ply and also the edges, before being fixed into position and used enough fixings.

I can understand the advice that you could have used plasterboard instead of ply. After all, if you have fixed ply into position then you could have done the same for plasterboard.

As Darrenba has said. You need a primer for the ply. PVA is a sealant and not suitable. The primer should be the one recommended by the adhesive manufacturer. Adhesive will have to be cement based powdered and flexible. Type will depend on what tiles you have, ceramic, stone etc. Grout also flexible.

Hi Guys

Thanks for your advice,

Ply is marine grade ply sealed on back and edges with Bal Bond SBR, fixed to existing studding through old lath and plaster with 70mm screws at 300mm centres, giving three perfectly flat walls at right angles to each other and the floor.

BAL website, "siteworks guidance page 9", recommends sealing back and edges with BAL Bond SBR. DO NOT seal faces to be tiled and fix tiles with BAL White Star ready mixed. I guess they must know what they are talking about, let me know if you think otherwise.

Sounds like a good solution to me, but happy to be put right if anyone has any experience of dramatic failures using this approach.

Those tiles are too large for white star

thanks for that, which Bal product would you suggest?

Probably Bal SPF would be ok. It comes in a bag not a tub.

I would fix cement backing boards to the ply before you tile, will give you a much better substrate to tile to. thunderbird1 is correct, I would have used plasterboard and tanked it. Using white star with tiles that size is definitely a disaster waiting to happen, tiles that size falling off and hitting someone could easily kill them. I would use rapid set flexible adhesive with those tiles

haveagohero wrote:I would fix cement backing boards to the ply before you tile, will give you a much better substrate to tile to. thunderbird1 is correct, I would have used plasterboard and tanked it. Using white star with tiles that size is definitely a disaster waiting to happen, tiles that size falling off and hitting someone could easily kill them. I would use rapid set flexible adhesive with those tiles

If I fix cement backing boards to the ply with screws, do I need to seal the ply face first.

Didn't use plasterboard on the advice of others, particularly a relative who owns a shopfitting company and who always uses ply when constructing walls.

Don't particularly want to take it down and start again, cement boards sound like they might make the best job from here.

p2ajb wrote:

haveagohero wrote:I would fix cement backing boards to the ply before you tile, will give you a much better substrate to tile to. thunderbird1 is correct, I would have used plasterboard and tanked it. Using white star with tiles that size is definitely a disaster waiting to happen, tiles that size falling off and hitting someone could easily kill them. I would use rapid set flexible adhesive with those tiles

If I fix cement backing boards to the ply with screws, do I need to seal the ply face first.

Didn't use plasterboard on the advice of others, particularly a relative who owns a shopfitting company and who always uses ply when constructing walls.

Don't particularly want to take it down and start again, cement boards sound like they might make the best job from here.

I'm concerned about the weight factor of adding cement boards to the ply do I need 12mm or as its fixed to a flat secure structure can I get away with 6mm?

6mm.

Although, if the ply is good quality far eastern and not the 5hit cheap far eastern then it will be fine to tile onto. You could even tank it first if you wanted.