DIY Granite Fireplace Surround

Disassemble the fireplace mantle, if there is one, and remove all trim from the fireplace. Spread a thin, even coat of thin-set mortar all over the surface of the fireplace surround with a finishing trowel. Allow this to dry for a full day.

Measure each flat face of the surround and cut out pieces of cardboard that correspond to these measurements to use as a template. Lay out the template pieces on a flat surface. Arrange the granite tiles atop each of the template pieces and note which tiles need to be cut; sketch the cuts on the backs of the tiles with a pencil and make them using a diamond-bladed wet saw.

Place the granite tiles back on the cardboard templates and finalize their arrangement so you are happy with how they look. Build a squared arch from 2-inch by 4-inch lumber that is approximately 1/2-inch taller than the space between the bottom edge of your fireplace firebox and the hearth but longer than the firebox on either end. Set this arch, or bolster, on the hearth so that it frames the fireplace opening and the top edge is lined up with the lower edge of the firebox. The bolster will act as a support for the tiles as the mortar is setting.

Smooth more thin-set mortar over the firebox area using a finishing trowel. Turn a notched trowel 45 degrees and drag it horizontally along the thin-set so that it is evenly lined. Place granite tiles over the firebox from bottom to top and from one end to the other.

Wait one hour to two hours to allow the thin-set to mostly firm, and then remove the wooden bolster. Tile the rest of the surround in the same way that you did the firebox, starting at the bottom and working up in small sections. Be careful to keep the tiles even and aligned.

Allow the thin-set to dry overnight. Use a round putty knife to lever out any loose scraps of the thin-set you find between the tiles. If your tiles are textured in any manner, cover the surfaces with overlapping pieces of painter's tape.

Apply grout all over the fireplace surround with a grout float, taking care to keep it level. Push the grout deeply between the tiles with the corners of the float, and use a pastry bag to work the grout in any nooks and crannies. Wipe the float clean and use the edge to scrape away excess grout; wipe the surfaces of the tiles clean with a damp sponge.