Over time, stone fireplaces can take on a grimy, sooty appearance. Stone may appear impervious, but it actually contains thousands of tiny holes throughout its surface. Eventually these holes can grab soot and fireplace dirt and hold onto them. Cleaning a fireplace takes patience and lots of scrubbing. Although some cleaning surfaces suggest using harsh cleaners such as trisodium phosphate, bleach or ammonia, this can damage the finish of natural stone. Instead use a cleaner formulated for stone fireplaces.
Cover the floor around the fireplace with dust sheets to protect the surface from dirt, grime and cleaning supplies.
Mix a heavy-duty alkaline fireplace cleaner with water as directed in a plastic bucket. Most cleaners require that you use 1 part water and 1 part cleaner.
Scrub the cleaner over an inconspicuous spot on the fireplace to test the solution. If the solution does not discolour your fireplace, it is safe to use.
Scrub the solution over your fireplace using a mop. Lightly scrub the solution over the worst stains with a scrub brush. Let the solution sit for 15 minutes to loosen grime, but do not let the solution dry.
Wash the solution free with a clean damp mop. Rinse the fireplace with clean water.
Seal the fireplace once you have cleaned it with stone sealer. The sealer will help prevent the fireplace from becoming grimy again in the future.