You have 4 inches of mortar on the ceiling?
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I am midway through a bathroom remodel and would like advice. We would like to install drywall over the current tile ceiling. The current ceiling consists of ceramic tile and three to four inches of mortar. I can drill holes through the current ceiling, allowing us to attach the drywall to the joists. I am, however, concerned about moisture. We do have a high-powered bathroom exhaust fan, which will be installed in the shower. It has a CMF of 110. This is significantly large for the 4' x 8' x 8' bathroom. We also plan to use waterproof paint on the drywall. Will this be sufficient to guard against the water vapor getting between the drywall and the tile? I have thought about drilling holes into the existing tile to allow any potential moisture to escape into the attic.
I have attached a photograph below of the current ceiling tile and fan. Any advice would be much appreciated!