How to Tile a Fireplace Hearth

Abide by Codes

Tiling an existing fireplace may not seem to be new construction in your home, but many local building codes will classify this renovation as new construction. You may even have to take out a permit before you do the work.

Building codes are understandably fussy when it comes to anything that concerns fire, so before you choose tile and purchase materials, check with your building code officials. For example, you may have to keep combustible materials, such as the mantel shelf, a specified distance from the firebox. Local codes may also require an inspection of your fireplace to make sure the damper and chimney are in good working condition. If they're not, the addition of a new metal insert may satisfy building code requirements.

Cut Bed

Hearths take a beating: A tiled hearth needs a sturdy 11/4-inch setting bed to withstand the shock of dropped logs. Make the bed from backerboard. Cut two strips of backerboard to the finished dimensions of the hearth. Use a carbide knife and a straightedge to cut the board to length and a circular saw with a masonry blade to notch any corners that have to fit around trim or the outside corners of the fireplace.

Embed Backerboard

Spread heat-resistant mortar on the existing hearth or subfloor and set one piece of backerboard in it. Embed the board in the mortar. Spread mortar on the top of the backerboard and lay metal lath in it. Then apply mortar to the second piece of backerboard and lay it mortared side down on the metal lath. Embed and realign this piece so the corners of both boards are flush with each other. Clean the excess and let the mortar set for 48 hours.

Extend the Hearth (Optional)

If needed, an extension to a hearth must be the same height as the original hearth or the new tile could crack. Measure the height of the existing surface and rip 2x lumber 11/4 inches thinner than that measurement. Adding two sheets of 1/2-inch cement backerboard and metal lath mortared together will bring the extension level with the original. Locate the floor joists and mark their positions on the floor. Fasten the 2x frame to the floor with screws that penetrate into the joists. Then fasten the first piece of backerboard to the frame, mortar it, embed the metal lath, and fasten the second piece of backerboard.

Install Trim

Cut and miter wood trim to frame the hearth using the same species as the surrounding floor, if possible. If not, stain and finish the trim to match the floor finish as closely as you can. Fasten the trim to the floor with 8d finishing nails. Countersink the nails and fill the holes with tinted wood filler.

Ease the Edges

Adding tile to an existing hearth will invariably raise its level above the existing floor. You can install square trim as shown above or apply eased edging with coped trim. Curved molding allows for a less abrupt transition between the floor and hearth and is easier to keep clean.

Set Tiles

Spread and comb heat-resistant mortar on the backerboard bed and, starting along an edge with full tiles, set the tiles in place. Be sure to leave a 1/4-inch gap along the wood trim. If your hearth design includes insets, set them as you go—don't wait until you've set all the field tiles.

Apply Grout and Sealer

After the mortar has cured (at least overnight), grout the joints with unsanded grout, cleaning the tiles thoroughly to remove the excess grout and haze. Caulk the joint along the trimmed edge and seal the tiles with a penetrating sealer. Apply the sealer liberally. It eases keeping the hearth clean.

Editor's Tip: Prevent cracked tile by using the hearth carefully. Some tiles stand up to the task of chopping firewood. Others don't. Ceramic and porcelain floor tiles are tough and should be able to take a beating. Saltillo and marble will crack. Marble also stains easily, so keep it well sealed to minimize black marks from sooty wood or thrown embers. Hang a high-quality glass or mesh screen. If a tile does crack, chisel it out and replace it.