DIY Marble Tile on an Uneven Fireplace Hearth

Sweep the hearth clean with a stiff-bristled broom, and then wash the area with a pH-neutral cleanser and sponge to remove any remaining dirt. Rinse with water and allow it to dry before continuing.

Mask off the hearth area with a strip of masking tape on all sides to mark the boundaries of the section that you’re tiling.

Measure the hearth area with a tape measure. Transfer the measurement to a cement backerboard and mark cutting lines onto the board with chalk to cover the hearth size. Due to the large size of cement boards, one will usually be large enough for any residential hearth. Score the surface of the board along the cutting lines with a utility knife, and then snap the board along the scored lines to cut it to size.

Place lines of construction adhesive onto the hearth area, about three inches apart and then place the backerboard in place over the adhesive. Press the board firmly to spread the adhesive as much as possible. Secure the board further in place by screwing it down with fasteners placed every 12 inches. Use a drill with a screw bit to place the fasteners through the boards and into the subfloor.

Find the firebox center by measuring the firebox width and dividing the width in half. Draw a line down the center of the hearth with a piece of chalk, using the center of the firebox as starting point. Draw a centerline across the length of the hearth perpendicular to the first line by measuring the hearth from the face of the fireplace to its front edge and dividing the measurement in half, then using a straightedge to make your chalk centerline at the desired mark.

Choose one of the two front boxed quadrants made by the crossing lines to begin the tiles. Dry-lay the tiles from the center line to the edge of the hearth along the hearth edge, using tile spacers for uniformity. Mark any tiles on the edge needing cutting. Continue to lay tiles in the desired pattern until you reach the centerline crossing the hearth from left to right. Mark a new centerline where the tiles cross the old one. Continue filling the hearth with tiles until complete. Mark the edge of tiles against the fireplace with cutting lines along their lengths to fit. Remove the tiles and place onto a flat surface in the same pattern they were in on the hearth so that you’ll know precisely where they fit.

Cut the marked tiles using a wet tile saw along the marked cutting lines. Place the tiles onto the saw’s cutting platform with the marked lines aligned with the saw blade. Turn on the water supply and then push the tile through the blade slowly to make the cut needed. Keep the water running while cutting the tiles to keep the blade cool. Wear safety goggles at all times while making cuts to avoid tile shard-caused eye injuries.

Mix the tile adhesive using dry thinset mix with latex additive instead of water. Mix the thinset with a mixing paddle until it is the consistency of peanut butter. Spread the thinset covering a single floor quadrant with a notched trowel and then angle the trowel over the spread material and drag the notches through to create ridges.

Place the marble tiles onto the thinset using the dry-lay pattern. Begin tile placement at the centerline and work your way to the edge of the hearth in rows. Place tile spacers in between the tiles to keep the joints of uniform size. After finishing one quadrant, check the level of the tiles with a carpenter’s level. Make adjustments by tapping high tiles into the thinset with a rubber mallet and placing additional thinset under low tiles. Allow the thinset to dry for 24 hours, and then remove all tile spacers. .

Spread grout into the joints between the tiles with a grout float. Move the grout into the joints by pushing it with the float edge over the tiles. Wipe the excess free of the tile faces with a damp sponge. Allow the grout to dry for two hours and then wipe with a piece of cloth to remove any haze.

Fill the joint around the edges of the tile surface with caulk the same color as the grout used. Create a smooth surface on the caulk using a wet finger to wipe away any irregularities. Allow the grout and thinset 72 hours' setting time before pulling up the masking tape and using the fireplace.