Installing Ceramic Tile Floor for a Fireplace

Cut the cardboard to the desired dimensions of the fireplace floor, using scissors. Ensure that the dimensions meet or exceed safety requirements. Place the tiles, spaced with tile spacers, onto the cardboard in the desired pattern. Use the marker to mark any tiles needing resizing to fit the design and leave the cardboard layout with tiles in place on the floor next to where the fireplace floor will go.

Even out the fireplace subfloor, if needed. Concrete or masonry subfloors should be evened out with a smooth layer of thinset mortar, around 1/4 inch thick, applied with a trowel. For plywood subfloors, cut a piece of backer board to the tile area size with a utility knife and set it in place with backer board screws and a drill every 6 inches on center. Apply a 1/4-inch-thick layer of thinset over the backer board and leave overnight.

Apply a 1/4-inch-thick layer of thinset over the prepared substrate, on the portion of the floor closes to the fireplace, on center, around five tiles wide. Furrow the thinset with the notched side of the trowel. Transfer the tiles from the cardboard design onto the thinset and gently press into the thinset, spacing with tile spacers. Continue laying and furrowing thinset and setting the tiles in place, working outward from the center until only the tiles requiring resizing are left.

Cut tiles that need trimming on the wet saw, feeding them gently through the blade, without much pressure. Spread thinset onto the backs of the cut tiles with the trowel and press them into position on the fireplace floor. Leave to set overnight.

Remove the tile spacers and apply grout to the tile joints. Hold the grout float at an angle to the tile joints so tiles don't pop out. Use the sponge to gently wipe away excess grout from the tile face as you go. Leave for 30 minutes after finishing, then wipe over once more to remove the last of the grout residue from the tile face.

Apply a line of caulk with a caulk gun around the perimeter of the ceramic tile fireplace floor, smoothing it over with a damp sponge or finger to create a tight seal. Leave to cure for three more days before lighting a fire in the fireplace, or continuing with the fireplace installation.