If a brick surround and hearth are stable and in good repair, you can tile over them. Clean them thoroughly, removing any soot, which interferes with adhesive; flatten any high spots with a rubbing stone. Spread a thin coat of heat-resistant mortar over the brick surface, leveling the mortar with a 2x4 set against 1/2-inch screed boards tacked into the mortar joints on either side of the opening. Let the skim coat dry and use it as a base for the tiles. If the surface is in poor repair or you don’t want to apply a skim coat, cover it with backerboard. Backerboard must be used when applying tile to a metal surround because most metal surrounds are not strong enough to support the weight of tile. If you plan to tile the surround, expect to spend four to six hours tiling. This does not including prep time. For the hearth, plan to spend about three hours tiling. Clean the fireplace and level the surface before you begin. Editor’s tip: If you want to tile the inside edge of the opening, use bullnose tiles and support them with a 2x4 batten until the mortar has cured. Push the “legs” of the batten just hard enough to keep it in place without compressing the tiles into the mortar.
