Seal the walls with a skim coat and let it dry thoroughly.
How to wall tile on plywood.
To install the concrete board apply tile adhesive to the back then press it down against the plywood.
Arrange the pieces so backer board and plywood joints don t align.
Sand with a medium grit sandpaper to create a uniform surface that s not too smooth.
Clean and heavily score area to where tiles are to be fixed it sounds like the adhesive does not have a rough surface in which to secure itself to.
The preferred method for tile installations is to use a sheet of underlayment.
If you are unsure if the floor is stable enough always fix tiles using an ultra flexible adhesive s2 like bal fast flex.
Mark the tile where it overlaps the installed.
While tile can be laid on plywood do not install tile directly onto the plywood subfloor itself.
You want the tile adhesive to have something to grab onto.
Spread thinset adhesive with a 1 4 inch notched trowel over the plywood subfloor.
You cannot install tile directly onto plywood because it is not dimensionally stable.
If you put tile directly on top of plywood it will chip and break.
Thoroughly vacuum the area and give the wall a once over with a damp sponge or cleaning cloth.
Use intervening layers of two sheets of plywood.
If you are tiling on a plywood floor with tiles above 400mm x 400mm in size or heavier tiles made of stone we recommend using an ultra flexible adhesive s2 such as bal fast flex.
To be sure maybe drill up to 6 evenly spread out holes in the plywood at least 4mm deep or straight through in the areas to be tiled so the adhesive sinks into the holes and hardens hence creating a stronger fix.
Use thinset with a higher latex content thinset is the wet base that you first trowel on the plywood to make the tile stick.
If possible you should always use concrete board underlayments rather than plywood.
Set the pieces of backer board into the adhesive.