The preferred method for tile installations is to use a sheet of underlayment.
How to lay tile on plywood wall.
To install ceramic wall tile use a level and measuring tape to mark the tile locations on the wall with chalk.
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.
Center your tile in the bathroom.
To install the concrete board apply tile adhesive to the back then press it down against the plywood.
If possible you should always use concrete board underlayments rather than plywood.
Wall preparation keep the installation surface clean and dry.
Step 4 center.
Use your drill to make this job simpler.
Laying tile to veneer plywood risks loosening and unbonding the veneer creating an unstable base for the tile.
Whenever you re laying tile on a wood subfloor you need to first install cement backerboard to prevent leaks and water damage.
If you put tile directly on top of plywood it will chip and break.
For wall installations plywood is overkill beneath the concrete or fiber board which is designed in five eighths inch material for wall settings.
Unlike wood or drywall sub surfaces cement backerboard will not rot warp or grow mold and mildew when exposed to water.
Then you want to install screws into the concrete board in each of the holes.
For the best results when tiling onto plywood floors follow these instructions.
Never install new tiles over existing tiles or onto an unprotected wood or plywood floor.
Do not install glass tile over particleboard chipboard masonite press wood plywood or asbestos surfaces.
Use long sweeping motions to apply mortar to the wall and start placing your tiles in the marked locations.
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.
Under british standards bs 5385 part 1 plywood has now been excluded as a suitable substrate material for the direct fixing of wall tiles therefore when tiling on to walls a tile backer board is required however tiling onto plywood floors is still acceptable under british standards.