How to Clean Natural Stone


Natural stone refers to stone that is untreated, unpolished and unsealed. This type of stone can be found on fireplaces and hearths, as pebbles in bathroom showers, as walls or short walls in indoor/outdoor areas and in many applications outdoors. Cleaning is most important around the fireplace because of the soot and smoke and outdoors because mildew and mold form in shady spots and outdoor rooms are susceptible to stains caused by food, wine, paints and stains. Cleaning natural stone around the fireplace and outdoors need to be handled differently.

Things You'll Need

  • Foaming bathroom cleaner Trisodium phosphate (TSP) Phosphoric acid High-alkaline cleaner Chlorine bleach Grout cleanser (optional) Diatomaceous earth Bar Keepers Friend Sure Klean Neutral pH stone cleanser Nylon brush Sponge Water and drying rags Drop cloths Bucket Plastic sheeting Steam cleaner (optional) High pressure water cleaner Muriatic acid Protective glasses, gloves, face masks

Cleaning a Natural Stone Fireplace

  • Move any close furniture, rugs and accessories away from the area. Protect the area where you will be working by using drop cloths around your immediate work area. Limit your intense cleaning to just those stones that need the cleaning. Do a less-intensive cleaning on the rest. Ventilate your room by opening doors and windows.

  • Saturate your stone and grout with water until they no longer absorb the water. If you try cleaning the stones when they are dry, the porous stone and grout may suck the newly liquefied dirt deeper into the stone and grout. By soaking the stone, the dirty liquid will stay on the surface.

  • Wearing protection, apply foaming bathroom cleaner and scrub. Remove the dirt quickly and don't allow streaks to run down the rock/grout face. Use your sponge to create a dam under the stone you are working on and clean up as you go. Depending on your stone style (river rock versus rough rock), this cleanser may be sufficient. If not, while your stones are still wet, use your steamer. Most steam machines have hand-held attachments and some have removable towels. These work well vertically as well as horizontally. Heat, cleanser and scrubbing will clean almost anything. Rinse the stone you are working on thoroughly and see how it's working.

  • Rinse your cleaned fireplace thoroughly. If it still needs more attention, use Sure Klean for fireplaces. Make sure your stones are thoroughly wet and keep them wet during cleaning. Follow the manufacturer's time suggestions.

  • Apply Bar Keepers Friend to affected areas in your grout after you've rinsed off other cleansers--never mix products. Follow the directions for the best result. You can apply a small amount of diluted bleach to persistent spots but remember that bleach lightens and changes the color of stones and grout so only do this for a specific problem. You can dilute TSP or phosphoric acid with water as a cleanser. Test in a remote area first. Bar Keepers Friend is not good for marble or metals.

  • Make a poultice of moist diatomaceous earth and your cleaning product. Mix the earth with diluted soap water from your bucket until it is wet clay. It should still hold together in a clump but be moist to the touch. Press your poultice into any persistent stain on your wet stones and cover the spot with plastic to keep it moist. The diatomaceous earth will draw out the stain. You can apply this with any cleanser that can sit on the stone for a period of time without causing problems. It works well with neutral pH stone-specific cleansers.

Cleaning Natural Stone Outdoors

  • Protect the area where you will be working by removing any flower pots, furniture or loose objects and covering larger shrubbery with drop cloths or plastic sheeting. Limit your intense cleaning to just those stones that need the cleaning. Do a less-intensive cleaning on the rest.

  • Saturate your stone and grout with water so that it no longer absorbs the water. Water your stone until it no longer accepts the water. If you clean the stones when they are dry, the porous stone and grout may suck the newly liquefied dirt deeper into the stone and grout. By soaking the stone, the dirty liquid will stay on the surface.

  • Wearing protective clothing, use your scrub brushes and a pH neutral stone cleaner/water mixture (as recommended for your application on the packaging). Try to remove and loosen the stain, mildew or mold as much as possible. Rinse frequently with clean water, and don't let dirty liquids run down your stones.

  • Apply muriatic acid (mixed as recommended on the package for your application). Remember that acids remove what they encounter, and you are only trying to remove a stain. Keep your work area rinsed well with a hose.

  • Use a high-pressure power washer if you don't need the muriatic acid and for general cleaning. Add pH neutral cleanser to the water to improve cleaning. Don't linger on stones or grout because power washers can reduce or loosen grouting. The power washer is generally good for reducing most outdoor stains, paints and marks. For high stain areas, consider applying a sealer to reduce future staining once your stones are clean.

Tips & Warnings

  • Clean stains quickly to prevent them from sinking in. Soot and smoke damage can be reduced by tossing salt into the fire. A custom-made aluminum pan under the grate can make ash removal quick and easy.
  • Many cleansers are caustic and protection must be worn to protect yourself while using the products. Never mix acid cleansers and bleach; you can die from the gas produced.

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