How To Remove Soap Scum from Natural Stone
Soap scum is a tricky combination stain that can result in hardened buildup, particularly if left untreated over a period of time. Removing soap scum from natural stone presents a special challenge, because many of the approaches that might work on another surface might be damaging in this case. Marble for example is sensitive to acids, and sealants on other types of natural stone surfaces might react unpredictably and undesirably with harsh cleaning remedies. This following is a very mild technique that requires a little extra elbow grease, but for the worthwhile reward of a soap scum free surface.
If the natural stone surface that you need to remove soap scum from is in the bathroom, run the shower at a hot temperature with the door closed to create a steam to loosen the soap scum residue.
In a plastic basin, mix a lightly sudsy solution with water and a mild pH neutral detergent like Ivory Liquid detergent. Apply the solution to the stone surface with a clean, soft sponge. Work a section at a time, refreshing the sudsy solution as needed to maintain cleanliness. Once the soap scum is removed, rinse well with water and use a squeegee to wick away extra moisture and avoid over-wetting and pooling that may damage your natural stone surfaces and encourage buildup. If the soap scum is combined with mold and mildew, substitute a lightly sudsy solution of borax and water for the pH neutral detergent solution, still following by a thorough water rinse and removal of excess water.
If the soap scum buildup is particularly crusty, use a clean sponge dampened with water to dab the soap scum affected areas with ammonia. Follow with the above pH neutral detergent method, and be sure not to let the ammonia rest for too long on the stain. Keep clean dry paper towels and rags handy to wipe up stray ammonia that may get on unprotected/unstained areas of the natural stone surface to prevent corrosion. The goal is to apply ammonia only to the soap scum stain, and avoid directly contacting any bare natural stone surface.
As a final resort, the entire surface can be treated with a lightly abrasive cleanser applied with a clean sponge dampened with water in a buffing motion. After polishing away the soap scum surfaces, clean with the pH neutral detergent method, rinse well, and squeegee to remove excess water. Allow the surface time to dry, and apply a commercially available sealant product that is appropriate to your particular natural stone surface, according to the manufacturer's directions.
Caution: Never mix cleaning agents or chemicals, the result can be dangerous or deadly. Before cleaning, always test the agent on an inconspicuous location to determine its suitability and to make certain it does not damage the material. Wear appropriate clothing such as gloves and protective eyewear, and work in a well-ventilated area.}