Stone seems impervious, but it actually has a porous surface that can be weakened by using the wrong cleaning products. Strong acid-based cleaners applied directly to your cast- or natural-stone mantel and fireplace surround can destroy their surfaces and cause permanent damage. Milder solutions should be used to get out tough stains. For common household dirt, a mixture of liquid dish washing detergent and water does the job. Products that safely clean concrete or masonry also work for your stone mantel and fireplace surround.
Preparing the Work Area
Protect the walls and floor area around the stone mantel before you begin. Adhere painter’s tape to the wall around the mantel to protect painted or wood surfaces against splashes. Lay a tarp or plastic on the floor or hearth area in front of your fireplace in areas where the surface may come into contact with the cleaning solution.
Supplies and Cleaning Solution
Gather a gallon bucket, a soft bristle brush, liquid dishwashing detergent and a bucket or bowl to mix the cleaning solution. Mix 3 parts water to 1 part mild dishwashing detergent or follow the directions on the label for a concrete or stone-cleaning product. For tough stains, mix 10 parts water to 1 part hydrochloric acid and a few drops of liquid dishwashing detergent. Hydrochloric acid is available at hardware, pool supply and home improvement stores. Wear gloves when you work with the mild acid solution and rinse immediately after cleaning to avoid discoloring the stone.
Soak The Mantel With Water
To avoid etching or burning the mantel’s surface with the water-and-acid mixture, presoak the area. Liberally apply warm water to the stone mantel with a sponge. As you work, make certain any stones or brick beneath the mantel stay soaked with water or are protected against splashes from the cleaning solution.
Cleaning the Mantel
A soft-bristle brush gently removes dirt, soot and soil after being dipped in the cleaning agent. Gently scrub the area and immediately rinse with clean water. Do not let the cleaning solution dry on the stone mantel or fireplace surround, as it could permanently affect the color of the stone. After rinsing with water, dry with a soft cloth or towel. Use a toothbrush to remove stubborn dirt from hard-to-reach corners or detailed areas.
Finishing and Sealing
Unless you have masonry experience, do not use muriatic acid in your cleaning solution, as it could leach materials up to the stone’s surface, etch its surface or leave burn marks or stains. After cleaning the stone mantel, apply a sealer meant for stone products to keep it from staining between cleanings. The stone mantel must be thoroughly dry before applying the sealant.