How to Replace a Slate Floor Tile

Remove the Old Grout

Scrape out the old grout around the broken tile, using a carbide-tipped grout saw. Be careful not to chip or scratch the surrounding tiles as you work. Use a gentle but firm motion to remove all of the grout until the side of the tile is completely exposed.

Break Up the Tile

Use a hammer to drive a nail set into the surface of the tile to puncture it in one or two places. This breaks the slate up so that you can remove it.

Remove the Tile Shards

Place the point of a cold chisel into one of the cracks and lightly tap the chisel with a hammer to loosen and pry up the pieces of the tile. Chisel very carefully near the edges of the tile to prevent damage to adjacent tiles. Break up just the tile and old mortar layers, being careful not to damage the subflooring or tile backer material below. 

Remove the Old Adhesive

Scrape away the old adhesive with a putty knife or cold chisel. Remove as much of the adhesive as possible, then use coarse sandpaper to remove residual adhesive and smooth the area. Remove all grit and dust from the floor with a shop vacuum. 

Place the New Tile

Mix a small batch of thinset mortar as directed by the manufacturer. Apply mortar directly to the back of the tile, using a 1/4-inch notched trowel. Drag the notched edge of the trowel through the mortar to make even ridges. Make sure that the entire bottom surface of the tile is covered. 

Set the tile in place on the floor and press it down until its surface is level with the surrounding pieces. You can twist it slightly back and forth to get it to sit down into the mortar. If desired, place a tile spacer at each of the four corners to ensure that your grout lines will be straight. Otherwise, simply align the tile by eye so the grout line is all the same width.

Tap Down the Tile

Lay a straight piece of a 2x4 board across the newly placed piece so that the board touches at least two adjacent tiles. Tap the board lightly with a hammer or mallet to press the new tile down so that it rests even with its neighbors. You can also use a level to ensure that you have the tile flush.

In the case of cleft slate, the surface of the tile may be irregular, making it impossible to get it perfectly even with the rest of the floor. Focus on getting the edges of tiles such as these even with adjacent pieces along the grout line.

Clean Up the Work Area

Use a small screwdriver to remove excess adhesive from the spaces around the tile. Wipe any smeared mortar from the tile surfaces with a damp cloth. If you used spacers, use a pair of needle-nose pliers to carefully remove them. Let the tile set for at least 24 hours. 

Grout the Tile

Mix a small batch of grout as directed by the manufacturer. Apply the grout to the space around the tile, using a putty knife. You can also use your fingers to force the grout down into the gaps. Wipe off any excess that gets on the surface of the tiles with a cloth.

When the grout does not yield to light finger pressure, carefully wipe over the grout lines with a wet sponge to smooth the grout and clean the tile surface. Rinse the sponge frequently in a bucket of clean water. It's fine if the grout leaves a haze on the tile surface. Let the grout dry overnight and seal it in the morning following directions on a good-quality grout sealer. Wait about an hour for the grout sealer to dry before moving on to the next step.

Clean and Seal the Floor

Clean the entire surface of the floor with warm water, making sure that you remove all dirt and debris. Allow the floor to dry thoroughly.

Apply a commercial-grade below-surface natural stone sealer to the entire floor as directed by the manufacturer. The sealer will soak into the stone, creating an invisible barrier and making the individual tiles shimmer with enhanced color. This will help to blend the new piece into the rest of the installation.