If you are looking for correct then the luan has to come up.
Ceramic tile over luan plywood.
Luan is a hardwood species containing extractives sugars.
It can also be used under hardwood laminate and carpet but this is much less common these days because subflooring is typically smooth enough for these materials many of which are installed with a different type of underlayment or pad.
Never have that under tile.
Plywood in ceramic tile installations.
I just finished prepping my 16 x 16 kitchen for ceramic tile.
I installed 3 4 plywood over the 5 8 underlayment.
The books says a minimum of 3 8 underlayment grade plywood no 1 4 then use ditra or a 1 4 cement backer board both are installed in a wet bed of thinset.
Luan plywood is an unacceptable and unapproved substrate to receive tile or cementitious backer units cbu.
Plywood underlayment is a thin plywood material that is most commonly used under resilient flooring materials such as vinyl and linoleum sheets and tiles.
I then installed 1 4 luan on top of this and was planning on attaching the ceramic tile to the luan.