Refacing a fireplace is a big job, any way you slice it. If you have a drab tile fireplace in need of a facelift, make sure you take the time to make any shortcuts successful. While you can't just stick a faux stone finish on top of tiles, it is possible to redo your fireplace without removing the tiles. It just takes the proper preparation.
Lay a tarp around the fireplace. Empty and clean the fireplace inside and out with a solution of 1/2 cup of oxygen bleach per 1 gallon of hot water. Allow the tile to dry.
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Sand the tile with a belt sander, starting from the bottom and working up, moving the sander in a circular motion as you go. The entire tile surface should be rough. Wipe the sanded tile with a dry microfiber cloth to remove the excess dust.
Mix a batch of thinset mortar as directed by the manufacturer. Apply a thin coating of mortar over the tiles with a trowel. Scratch the surface with a hand rake. Allow the scratched coat of mortar to dry overnight.
Prepare a fresh batch of thinset mortar. Spread the mortar on the back of one of the stone tiles and press it against the sanded tile surface near an upper corner of the fireplace. Hold the stone tile until it stays in place. Repeat with the rest of the stone tiles, working downward, to cover the fireplace. Wipe off any wet mortar with a sponge. Allow the mortar to dry completely.
Scrub away any dried excess thinset mortar with a wire brush. Mix the grout mortar as directed. Fill a grout bag halfway with grout mortar. Hold the bag at a 45-degree angle with the tip touching a space between stones. Squeeze the bag gently and pipe the grout between the stones, refilling the bag as necessary. Smooth the grout with the edge of your trowel as you go. Allow the mortar to set for 48 hours before using the fireplace.