One wall of my shower is onto a plywood sheet. Some of the tiles are
loose and I want to redo them. I think part of the problem may be that
the plywood is too thin and flexes. I might replace with thicker
material but what type of tile adhesive works best?

I've used a flexible adhesive on wooden floors, but I'm not sure if
this is suitable for walls.

andyv wrote:
One wall of my shower is onto a plywood sheet. Some of the tiles are
loose and I want to redo them. I think part of the problem may be that
the plywood is too thin and flexes. I might replace with thicker
material but what type of tile adhesive works best?

I've used a flexible adhesive on wooden floors, but I'm not sure if
this is suitable for walls.

No matter how thick the adhesive you put on if the ply flexes then the
tiles will become loose again.

Is there enough space to put(screw/nonails)plasterboard over the plywood?

--
Sir Benjamin Middlethwaite

One wall of my shower is onto a plywood sheet. Some of the tiles are
loose and I want to redo them. I think part of the problem may be that
the plywood is too thin and flexes. I might replace with thicker
material but what type of tile adhesive works best?

Ply should be at least 18mm thick. If not, it is not suitable.

Use a good flexible adhesive. I would use BAL White Star for this
application.

Christian.