"Stones are basically sponges," says Fred M. Hueston, director of the National Training Center for Stone and Masonry Trades, in Longwood, Florida. He's working in a kitchen, mixing up an odd-smelling poultice of flour and hydrogen peroxide in the hope of removing a stubborn coffee stain from an island countertop. Spread over the stain, the paste should literally pull the discoloration out of the red travertine. "Granite, marble, and limestone consist of interlocking mineral crystals with pores between them," he explains. "So spills soak into unprotected stone in just 15 to 20 minutes for granite, and 30 minutes to an hour for marble and limestone." The liquid evaporates, but a mark remains.
Hueston, who literally wrote the book on the subject of stone restoration (Stain Removal Guide: For Stone, Tile, and Concrete), will leave the poultice in place for 24 hours. This will allow it to "wick" the stain out of the countertop, in the same way that poultices made with other ingredients pull oil stains out of concrete or venom out of snakebite victims. He determines his recipe on the basis of the stain and stone types: an absorbent base like dry clay, flour, or a paper towel, and a wicking chemical such as detergent, bleach, or hydrogen peroxide. If the countertop has been both stained and etched, the stone must be polished and a new sealer applied. "Cleaning spills right away and using coasters is a lot easier," he says.
Preparing the poultice
Fred Hueston mixes flour and hydrogen peroxide to create a poultice that's about the consistency of creamy peanut butter. Peroxide works best for food stains, but in the case of cooking-oil stains, Hueston uses dishwashing liquid, which breaks up the oil. For biological stains — mold, mildew, fungus — he uses household bleach. (The chlorine doesn't bleach the stone, only the stain.) Rust disappears with sodium hydrosulfate, available in over-the-counter rust removers. "I've seen stains go from light yellow to deep purple with the wrong chemical," says Hueston. He always tests the poultice on an inconspicuous spot on the countertop before applying it to the stain.
Apply the poultice
Applying the poultice is something like icing a cake. Using a plastic putty knife, Hueston spreads a quarter-inch layer of the paste over the stain and beyond it by a quarter of an inch or more. The older and darker the stain, the longer he leaves the poultice in place and the greater the likelihood he'll need to repeat the process. If the stain is less than a day old, a single application may work in 10 hours, but for most stains Hueston waits 24 hours just to be safe. For generations-old discoloration in historic buildings, he has used as many as 15 poultices over 2 to 3 weeks.
Cover the wet poultice
Covering the wet poultice with a sheet of plastic wrap slows the drying process of the active chemical. Hueston fastens the edges to the countertop with blue painter's tape. (Regular masking tape is too sticky and may remove sealer or even dull the stone surface when it's pulled up.) Then he pokes several small holes in the plastic wrap so that some air can circulate around the poultice, allowing it to dry and to draw the stain out as it does. When the poultice is dry, Hueston removes the tape, and the plastic with it.
Scrape of poultice remains
Once the poultice is dry, its useful life is over. He scrapes the remains off the counter with a putty knife. The result gradually becomes apparent — like the classic movie scene where the doctor unwraps the gauze after plastic surgery. Hueston wipes the surface with a dry towel and is pleased to see that the stain has disappeared. If there's a ring around the newly cleaned area, it's residual moisture that should evaporate within a few weeks. To expedite the drying process, Hueston sometimes will sprinkle a bit of dried poultice over the spot.
Polish the surface
Hueston uses a polishing tool and marble-polishing powder to smooth the surface, which was etched by the acidic coffee. He attaches a polyester polishing pad to the Velcro drive plate, then spreads the gritty polishing powder over the surface and splashes on a tablespoon of water. For marble and limestone, he sprinkles an abrasive powder made from aluminum oxide and oxalic acid; for granite, he uses a tin oxide powder. He works the powder over the rough stone, moving the polisher in small circles. When he feels the resistance ease, he stops and wipes the surface with a dry cloth, then visually inspects the area and glides a hand over it to check for smoothness.
Seal the surface
Because the poultice and the polisher remove the sealer, Hueston must recoat the stone. There are two choices: Topical sealer, a paste wax coating, is used on marble and limestone because it protects these relatively soft stones from etching caused by everyday kitchen substances like citrus juice. Penetrating sealer is for stones such as granite that don't react with acids and therefore don't need protection from etching. It soaks into the stone, where it provides protection from stains. Because it doesn't form a surface coating, it is less prone to wear caused by everyday use of the surface. For marble countertops, Hueston recommends using both types. To apply penetrating sealer, he pours a shallow puddle onto the countertop and lets it soak in for 10 minutes before hand-buffing the area with a lamb's wool pad like that used for polishing a car. The counter can't be used for 6 hours. For a topical sealer, he buffs the coating on and off as if it were car wax. Sealers should be reapplied at least once annually.