Hello, I'd really appreciate some expert advice.
We have replaced a rotten chipboard floor and badly mildewed wall in the bathroom with marine plywood. Extra noggins have been placed to provide improved rigidity under the floor ply.
When I was asking about suitable adhesives today in a tile shop one of the staff commented that tannins in the ply could leach into the grouting over a period of time and cause discolouration, which I'm now very worried about.
Is it possible to seal the ply prior to tiling/grouting to prevent this happening? If so, what woudl you recommend for this?
We will be using white ceramic tiles around the bath and shower areas, and slate on the floor.
Any comments, thoughts, suggestions or advice most welcome.
Thanks, Leigh

For the floor a flexible adhesive would be suitable and after the required setting time grout with flexible floor grout. Priming the surface of the ply is not usually advised but the back and edges will need priming (NOT PVA). Read the info on the adhesive you will be using.

As for the walls i would either replace or overboard witha a tilebacker board of some sort.
I would take a guess that the tile shop you spoke to would be selling "No More Ply" backer boards as the info you have been given is almost word for word out of their brochure.