After removing the wall on the jacuzzi, I have a better idea of what the floor is really composed of. It looks like there is a 12/16" or
13/16" plywood over the joists, then there is 8/16" or 9/16" plywood over the first layer.
The second layer is more or less level with the carpeting in the master bedroom. I would like to keep the master bathroom as close to level as I can with the master bedroom level. If I put 1/4" or 1/2" cement board on top of the 2nd layer of plywood, I think the change will be sore to look at and will be a tripping hazard
Can the second layer or plywood be replaced with 1/2" cement board?
Some research on the internet makes me think that it will not be a problem for ceramic tile surface cracks.