Generally, ceramic, porcelain, and stone tile can be installed on interior walls that are structurally stable, on plane, and consist of a suitable substrate. Suitable substrates include masonry, backer-board, gypsum board (drywall), or mortar beds. Many people, including professional tilers, like to use good quality mastics due to their extended pot life and their extended "on the wall tiling time." Good quality mastics can be applied on the wall and still be able to hang tile twice as long as portland cement thinset of equal quality. Caution must be exercised that the mastic does not "glaze over" rendering the mastic too dry to bond the tile to the wall.