Change or update the look of a room by remodeling your fireplace surround. You can alter the appearance of a marble fireplace surround by applying tile over the existing marble stone. When you tile over marble on a fireplace, you must first rough the surface of the marble so that the tile thinset will have a good bonding surface.
Sand the entire surface of the marble with 30-grit sandpaper, working in circular motions. This will give the marble surface an etched texture so that the tile thinset will adhere properly.
Run a dry shop vacuum to remove all sanding dust from the marble fireplace and surrounding areas.
Lay a piece of plastic sheeting on the floor surrounding the fireplace work area. Place the tiles on the plastic sheeting to create a dry run, or design mock-up. The dry run will allow you to choose the desired pattern or design of the tiles before adhering them to the fireplace.
Draw or snap a chalk line where the top of the first row of tile will set.
Pour tile thinset into a large bucket and mix it with water. Refer to the directions located on the thinset bag for the water mixing ratio. Start with a small amount of mixed thinset, only enough that you can use within one hour.
Dip the trowel into the thinset mixture, and scoop out a trowel-full. Spread a 1/4-inch thick layer of thinset over the marble, starting in the center of the fireplace surround and below the line you set as your level point. Use the notched end of the trowel to groove the thinset layer.
Press the first tile into place on the layer of thinset, and give it a wiggle to bond it to the thinset. Cut any tiles that need cutting to fit within the fireplace with a wet saw. Place tile spacers evenly around the sides of the tile. Press more tile pieces into place within the remaining thinset, working your way out from the center and placing tile spacers around each tile until you have completely covered the marble. Allow the tile thinset to dry overnight.
Remove all the tile spacers between the tile. Mix tile grout in a large container according to given directions. Fill the grout bag three-fourths of the way full with the mixed grout. Force the grout into the open tile joints by squeezing the grout bag. Smooth the grout lines by dipping a finger in water and running it along the tile joints. Allow the grout to set for at least 30 minutes.
Wipe the excess grout off of the face of the tiles with a dampened sponge. Allow the grout to dry for 24 hours. Use a dry cloth to wipe off any grout haze.
Use a paintbrush to apply a thin layer of grout sealer as directed by manufacturer. Wait up to 48 hours for the grout sealer to dry.