Mosaic fireplaces are made by applying mosaic to the surrounding face, but not the inside of the fireplace itself. In fact, if the fireplace is actually used and not merely decorative, you probably shouldn’t mosaic the hearth (floor) in front of the fireplace because heavy chunks of wood and fire irons tend to crack and knock tile loose over time. That being said, porcelain tile and many varieties of stone are very hard and could be used for the hearth. The fireplace surround can be mosaiced with a variety of materials including glass tile.
Brick and stone should be plastered over with thinset mortar to smooth the surface in advance of actually applying the mosaic. Alternatively, 1/2 inch concrete backer board can be mounted over the existing fireplace surround as a backing for your mosaic.
For mounting the tiles, a white PVA adhesive such as Weldbond or thinset mortar should be used. I have written a page for using thinset mortar for detailed mosaic art, but for larger tiles, the thinset could be spread with a 1/4 inch notched trowel, and the tile pressed into it relatively quickly as is typically done with bathroom tiling.
A Whimsical Fireplace Mosaic
The fireplace mosaic below is a whimsical design made by my friends for their ice cream shop, which was located in a restored Victorian house in Decatur, Georgia. The color choices and motifs are in keeping with the kid-friendly theme of their shop.
An Outdoor Fireplace Mosaic
For outdoor mosaics subject to rain, humidity and freezing temperatures, thinset mortar should be used instead of adhesive to mount tiles. Thinset is a sticky concrete product that contains polymers for added strength and adhesive properties. We usually use it for grouting our outdoor mosaics because it is stronger than grout, and it will be the same color as any thinset that squeezes up between the tiles from when they were attached. We have successfully dyed thinset with concrete dye without any noticeable loss of strength or adhesion. Concrete dye and thinset are sold at most building material stores.
The fireplace below is actually an outdoor pizza oven, based on the wood-fired Italian variety, and the mosaic is on the hearth in front of the oven. The oven and the mosaic were made by one of our customers and her boyfriend in his backyard. “I Cinquanta Gradini” means “The Fifty Steps” in Italian, a reference to the 50 steps leading up to the house and oven.