Celebrating a Lesser-Known Role of Hamilton: Father of the Coast Guard 2 Â· 1 comment President Trump to give keynote speech at US Coast Guard Academy in May 2017.
First, You don't Tile over Drywall in any case in Bathroom area exposed to Moisture etc.( you may have to remove existing drywall& install cement board, around that area for better results of tiling. Second. The drywall should not be, less then Blue Board for all areas except Shower or bathtub tiling.
If you're setting the tiles on a 1 1/2 thick mortar bed, you're not tile directly on plywood. Tiles can, but should not be installed directly on plywood. Even then you would require a double layer of plywood. It's one of the methods recognized in the industry, but only in dry areas and with many precautions. High failure rate.