According to backer board manufacturers and tile setters installing backer board directly over an old solid wood subfloor is risky for a couple of reasons.
Attaching tile to plywood wall.
However the floor must be properly reinforced to minimize flexing.
While tile can be laid on plywood do not install tile directly onto the plywood subfloor itself.
Use thinset with a higher latex content.
You may also want to tile an outdoor shed or tile plywood boards for display.
Then i would remove any loose tiles and scrap away any adhesive that is left on the ply and tile you want the ply and tile to be perfectly clean for the next stage.
There may be times when you want to bond tile directly to plywood or another wood surface rather than screwing down backerboard first.
Level the surface using a wood filler.
Unscrew switch plate and outlet covers and set aside.
First changes in humidity make solid wood shrink swell and cup more than plywood.
For flooring use intervening sheets of plywood.
How to glue tile to wood.
For wall installations plywood is overkill beneath the concrete or fiber board which is designed in five eighths inch material for wall settings.
Unscrew register covers and save the screws.
You can bond tile directly to a plywood subfloor and expect it to last.
If possible you should always use concrete board underlayments rather than plywood.
Then in either case the subfloor should probably be about an.
The silicone or urethane adhesives should work too but the thin set mortars are easier to work with and easier to get full adhesive contact between the tile and its substrate.
Backerboard can double the thickness of an installation which can be troublesome in some locations.
Space the field and edge fasteners.
Tips for laying tile on plywood subfloor.
The preferred method for tile installations is to use a sheet of underlayment.
Remove any obstacles from the installation area.
The joists if they re 2x8 newer code and not 2x10 older code must be braced every four feet with cross braces which minimizes independent flexing of each joist and the subfloor above.
There are thin set dry set mortars design specifically for adhering ceramic tile to plywood that is designated as an ansi a118 11 thin set mortar.
Fill in all large gaps and holes as these will prevent proper adhesion of the tiles.