Tiling your fireplace can dramatically change the look of the entire room. Many people choose to place tile only on their fireplace surround, but you can add tile to the inside of the fireplace opening as well. You also have the option to tile only the inside of the fireplace for a different look. Most ceramic and stone tiles are appropriate for fireplaces, but you must use heat-resistant adhesives.
Measure and cut backerboard to cover the surfaces you will tile. Attach the backboard to the inside of your fireplace using a power drill and the appropriate screws. Use masonry screws if the subsurface is brick, and metal screws if your fireplace interior is metal.
Spread mortar on the backerboard covering one side of the fireplace. Comb the mortar with the edge of the notched trowel to make grooves in the mortar. Press your tiles into the mortar, placing tile spacers between them. Repeat for the other side of the fireplace and then the top.
Place a 2-by-four inch piece of wood under the tiles covering the inside top of the fireplace. Brace the wood in place with two 2-by-4 inch pieces of wood placed vertically on either side of the fireplace, creating a batten. Position the legs of the batten so that the upper tiles are supported, but not pushed into the mortar.
Let the mortar cure overnight. Remove the batten and the tile spacers.
Spread grout into the spaces between the tiles using a grout float. Scrape away the excess grout from the tile surface using the edge of the grout float. Joint the grout by running the corner of a damp sponge along all the grout lines. Clean any remaining grout from the tile surface with a wet sponge before the grout dries.
Let the grout dry overnight before lighting a fire in the fireplace.