So the tile in the shower stall in my home was built by the previous owner over drywall. There is serious damage up the bottom foot of drywall which I've torn out already. However further up the remaining 5 feet the drywall and tile appears to be fine. I have not demo'd that portion yet. I know drywall for showers is sacrilege but was pondering adding cement board to the bottom foot and retiling over that. Am I crazy or could this work?