How to Cover an Existing Fireplace with Granite

Start with a smooth surface on the fireplace surround and remove any mantles and trim. Cover rough surfaces, such as brick or rock, with a level coating of thinset (an adhesive mortar) using a finishing trowel so that the surface is even all over. Let the thinset dry for 24 hours.

Measure the fireplace surround and use these measurements to create a cardboard template of the area. Place the template on a flat surface and lay out the granite tiles so that you can see where trim cuts need to be made; remember to leave space for grout lines. Mark the planned cuts with a pencil and use a diamond-bladed wet saw to make each one. Make sure you wear safety glasses when using the saw.

Position the tiles on the template again and make sure you are satisfied with the look of the layout. Prepare a wooden bolster for the tiles that will be placed onto the firebox, the horizontal area at the top of the surround. Cut three 2-by-4 boards so that they are about one-half inch taller than the distance between the hearth and the bottom edge of the firebox and longer than the firebox from end to end.

Hold one board straight up and place another flat. Set the end of the tall board against the face of the flat board and clamp them together; position the third board up and down and clamp it to the other end of the flat board. Nail the boards together and remove the clamps.

Place the bolster on the fireplace hearth, just outside of the fireplace opening so that the top edge is aligned with the bottom of the firebox. Apply new thinset horizontally over the entire firebox area with the edge of the finishing trowel. Comb over the thinset with a notched trowel to create texture.

Tile the firebox with the granite tiles, starting with the lowest center ones and working upward, then alternately side to side. Remove the bolster once the thinset beneath the firebox tiles has set. Apply textured thinset and granite tiles to the rest of the surround, working in sections from the bottom up and adjusting the tiles by hand to keep them straight and even.

Let the thinset dry well. Pry out any loose bits of thinset caught between tiles with a rounded putty knife. Cover any tiles with raised or patterned surfaces with layers of painter's tape.

Spread grout over the entire tiled surround with a grout float, working the grout down into the spaces between the tiles; apply grout between raised or textured tiles with a pastry bag. Turn the float 45 degrees and drag the edge across the tiles to remove excess grout from the lines. Clean the surface of the tiles with a damp sponge.