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Cleaning Limestone Steps

House Doctor | Gary Dymski

September 19, 2002

Q. I have limestone steps in front of my house, which faces east. The steps are discolored, a green with brown spots. I have tried scrubbing with a pine-based cleaner and bleach without success. Do you have any suggestions as to what I can do to correct this condition and then prevent it from happening?

- Tom Harrison, Merrick

A. Your limestone steps can indeed be successfully cleaned, but stay away from chlorine bleach and other harsh cleaners. Limestone is a natural stone that can dissolve and break down if not properly maintained. There are several types of commercial cleaners and sealers for limestone available at masonry supply and building supply stores.

One such family of cleaners is made by Prosoco (www.prosoco.com), a Kansas- based manufacturer of masonry cleaners often used in restoring and maintaining the limestone and other natural stone contained in the exteriors of historic buildings. Prosoco products were used in cleaning Grand Central Station, buildings on Ellis Island and the Empire State Building, says Scott Buscher, Prosoco director of marketing.

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Buscher advises a milder approach with limestone steps. A cleaner like Prosoco's Enviro Klean 2010 would be his first choice for homeowners. Prosoco cleaners and sealers are available at Kenseal Construction Products in Long Island City (718-937-5490).

Here's some more information that might help in the maintenance of your limestone steps. First, limestone should be treated with cleaners made from two ingredients: a non-ionic detergent and an alkali, like ammonia and baking soda. Kodak makes a non-ionic detergent called Photo Flo; it's available at photographic shops. Some cleaners made by Simple Green (www.simplegreen.com) also are non-ionic. (Non-ionic detergents are neutral cleaning agents that do not contain or form soluble salts; check the cleaner's label.)

The cleaners mentioned above have been used by several groups involved in the preservation of historic buildings. Their advice is to use a solution of one ounce of cleaner in five gallons of water. Wet the stain with water, then scrub in the solution with a thick, natural-bristled brush with a wooden handle. (Nylon bristles and plastic handles may cause discoloration in the stone.) Let sit for a few moments (don't let it dry), then rinse. Repeat if necessary.

Before using any product on the stain, try testing it on an obscure area first, Buscher says.

Genealogy experts, those who clean old, blackened gravestones, say a non-ionic cleaner called Orvus, which is used to bathe cattle and horses, is excellent for limestone. Orvus also is used to clean fine rugs because it will not discolor dyes, and it will not irritate the eyes of animals.

Mix a solution of one tablespoon of Orvus, one cup of ammonia and a gallon of water. Apply the Orvus solution in the same manner - be sure to wet the steps with water first - and repeat if necessary. You can get Orvus at tack shops (under Saddlery & Harness in the Yellow Pages).

Once the stain has been removed, seal the steps with an impregnator. Again, such sealers can be purchased at masonry supply stores.