(Also see Substrates)
Drywall has a paper or water-resistant covering over a core that is made of gypsum. It is a common building material used to construct interior walls in dry areas. Drywall should be installed in strict accordance with the manufacturer’s instructions and local building codes. It is best suited for interior dry areas only, as some building codes restrict the use of drywall and do not permit it to be used for shower walls or tub walls.
Drywall seams are patched and filled with a gypsum-based patching compound commonly known as “wall mud.” Because gypsum and cement are not compatible, it is important to prime all drywall surfaces with a primer such as MAPEI’s Primer T prior to installing tile.
If drywall has been painted, it is best to cover it with cement board or remove and replace it with new drywall or new cement board.