How to remove pet urine stains from slate and other stone surfaces

Q: How can I remove cat urine stains from slate?

A: The best advice about pet urine stains on stone is to avoid them — and the stink that can persist for what seems like forever — by cleaning up puddles as soon as possible. Blot up the liquid with paper towels, rather than wiping it, to avoid spreading the urine onto a wider area. Then, with fresh paper towels at each step, wash and rinse using the same blotting technique. For the wash, mix a squirt of hand dishwashing detergent — about a quarter teaspoon — in a quart of warm water. Blot it on, wait a few minutes, then blot off. Rinse by repeating this process several times with plain water.

Of course, if the slate is already stained, a quick cleanup won’t be enough. You still should be able to eliminate or at least greatly reduce the stain, though. The stone stained because it was porous enough to absorb the urine and the urine dried while trapped there. You need a way to reverse that process and suck out the stain. Your best bet is a poultice — a highly absorbent powder mixed with liquid suited to the stain. If you spread the poultice over the area and keep it wet long enough to allow it to sink in and dissolve the stain ingredients, the mixture will pull those ingredients toward the surface as it evaporates, trapping them in the drying powder.

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A poultice recipe recommended by Surface Care Pros, a training and marketing resource for stone care professionals, calls for mixing white flour or diatomaceous earth with hydrogen peroxide in the “20 volume” concentration. This type of product, sold for bleaching hair, consists of 6 percent hydrogen peroxide in water, double the percentage in the hydrogen peroxide sold at drugstores as a disinfectant. Find the higher potency product at a local beauty shop, or order it online. A 16-ounce bottle of Salon Care 20 Volume Clear Developer is $9.03 on Amazon, but online delivery takes a while because the product has to be shipped by ground. (Hydrogen peroxide isn’t flammable on its own, but it is a powerful oxidizer, meaning the oxygen it releases can make other substances burn more intensely and even explode.)

Diatomaceous earth, made by grinding fossilized algae, is sold for many uses, including as a gardening aid. The particles’ sharp edges poke into many kinds of crawling insects and cause them to dry up and die. A four-pound bag of Harris brand’s diatomaceous earth crawling insect killer is $10.26 at Home Depot. If you use flour, choose ordinary white flour.

When you’re ready to tackle the stain, dampen the area with distilled water to begin dissolving the remnants of the urine. Wear protective gloves and glasses, and work carefully to avoid stirring up and inhaling dust if you are using diatomaceous earth. Put some of the powder in a glass or ceramic container; the amount depends on the size of the stain. With a plastic or wooden spoon, stir in enough hydrogen peroxide to make a thick, creamy mixture, sort of like warm peanut butter. Be careful not to get it on other surfaces, and don’t get any in your eyes or on your skin or clothes. If you do spill, rinse immediately and thoroughly.

With a plastic putty knife, spread the poultice about a quarter-inch thick over the stained area, including about an inch beyond the borders. Then cover it with plastic wrap, and tape down the edges with painter’s tape. Cut a few small holes or slits in the plastic. When the poultice is completely dry — this may take 24 to 48 hours — scoop up the powder with the putty knife. Rinse the area with distilled water and allow the slate to dry. If the stain is less noticeable but still not gone, repeat the process. You may need to do it a half-dozen times. Stop when you no longer see improvement.

Even once the stain is gone, you may still smell urine. Try an enzyme product sold for eliminating urine smells in carpets, such as Rocco & Roxie stain & odor eliminator ($19.97 for a 32-ounce bottle on Amazon). Surface Care Pros recommends spraying the cleaner on liberally, then covering the area with plastic wrap to slow evaporation and give the enzyme more time to work. After an hour or two — or maybe longer if the air in your house is vey humid — pull back the plastic and blot the floor dry with paper towels. The paper towels should look and smell like they picked up urine. Wait one to two hours, then apply the cleaner a second time using the same procedure. Repeat as necessary.

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