If the structure is adequate the use of a cement based floor patch that allows for the needed height may be the best choice.
Tiling over plywood underlayment.
Void free underlayment grade panels which both stiffen the existing floor and provide uniform support to prevent cracks in the tile above.
Use intervening layers of two sheets of plywood.
The plywood will expand and contract at a different rate as the tile causing cracks to develop in the grout lines or tiles over time.
While tile can be laid on plywood do not install tile directly onto the plywood subfloor itself.
Tape over holes and cracks in the wood subfloor or slab before pouring on the self leveling tile underlayment to keep it from seeping through and leaving indentations.
For residential use one form of underlayment the tile council of north america s handbook allows is plywood over joists that are 16 in.
Once properly in place and cured the tile can be installed.
Once the surface is completely covered cover the adhesive with the fiberglass based paper and smooth out any wrinkles or bubbles with a broad drywall knife.
A tapered piece of plywood may be difficult to fabricate and may not offer the support required for a good installation.
Fill seams in the subfloor with caulk.
On a plywood subfloor you need either a layer of cement backer board or an underlayment membrane like custom building products wonderboard and redgard between the subfloor and tile for the thin set adhesive to achieve a good bond.
No matter how firm the subfloor.
Tape off any affected vents with painter s tape.
This prepares and seals the surface for the.
Begin by applying the thin skin adhesive to the plywood with a smooth trowel.
The go to product is 1 2 in.
Use thinset with a higher latex content thinset is the wet base that you first trowel on the plywood to make the tile stick.