Even with proper ventilation, shower steam exposes bathrooms to more moisture than any other room in the house. Bathrooms require materials that will not leak or hold moisture that damages underlying framing materials. The materials must also repel water so they do not breed mold and mildew. While the ceiling in a does not get the same exposure as the floor, it is still exposed to water.
Water Resistant Sheet
Water resistant sheet rock is available, and is usually called "greenboard" because of its green hue. While it may be referred to as water-proof, greenboard is not. The material is moisture-resistant. It is a better alternative to cover bathroom walls and ceilings than regular gypsum or because of its water resistance. Like regular sheet rock, it should not be used as a sub-straight for tile.
Vapor Barriers
A vapor barrier is critical element in tiled bathrooms. Even thoroughly grouted tiles are not water-proof. Water (and some tiles) will wick water through to the substrate, so a water-proof membrane, or "vapor barrier," must be installed in between the tiles and whatever substrate or "backerboard" is used on shower stall floors, walls and ceilings. Tile ceilings benefit from vapor barriers because they are particularly prone to moisture from condensation.
Waterproof Substrates
Substrates, or "backerboard," for shower and bathroom tiles are not always water-proof. If they have been water-proofed with a vapor barrier, they probably do not need to be. Using water-proof material in addition to using structural backerboard instead of sheetrock gives you extra insurance against structural damage, mold and mildew. Cement board, which is a cement-infused mesh sheet, is a common water-proof substrate. It prevents water damage from condensation when used for tile ceilings in or near shower stalls.
Tiles
Some tiles are porous and not well-suited for bathroom and shower applications. Glazed ceramic tiles have a number of advantages over porous materials. While water may wick through ceramic, it will not permeate ceramic glaze. The ceramic finish is also easy to clean and is an inhospitable environment for mold, mildew and bacteria. This can be particularly helpful on ceilings where droplets of condensation may actually remain longer than beads of water on a wall; Moisture on the walls tends to run down the wall instead of beading up until they evaporate.
Tags: mold mildew, sheet rock, vapor barrier, from condensation, shower stall, walls ceilings