Definition And Use. Applied to stone to remove stains, a poultice is a chemical or mixture of chemicals combined with an absorbent material, forming a thick paste. The poultice is spread over the stained area to a thickness of about 1/4″ to 1/2″ with a wood or plastic spatula or scraper covered with plastic, and left to work for 24 to 48 hours. The chemical will draw out the stain into the absorbent material. Poultice applications may have to be repeated to thoroughly remove a stain, but some stains may never be completely removed.
Poultice materials include kaolin, fuller’s earth, whiting, diatomaceous earth, powdered chalk, white molding plaster, and talc. Approximately one pound of prepared poultice material will cover one square foot. Do not use whiting or iron-type clays such as fuller’s earth with acid chemicals; the reaction will cancel the effect of the poultice. A poultice can also be prepared using white cotton balls, white paper towels, or gauze pads, which may be more effective when using highly volatile solvents such as acetone or mineral spirits. Premixed poultices that require adding only water are also available from stone maintenance supply companies.
Poultice Mixtures For Various Stains
- Oil-Based Stains. Poultice with baking soda and water or one of the powdered poultice materials and mineral spirits or a commercial degreaser.
- Organic Stains. Poultice with one of the powdered poultice materials and 12% hydrogen peroxide solution, or use acetone instead of hydrogen peroxide.
- Iron Stains. Poultice with diatomaceous earth and a commercially available rust remover. Rust stains are particularly difficult to remove; professional assistance may be required. Many rust removers contain acids that will etch marble, limestone, and certain granites.
- Copper Stains. Poultice with one of the powdered poultice materials and ammonia. These stains are difficult to remove; professional assistance may be required.
- Paint Stains (Water-based). Poultice with one of the powdered poultice materials and a commercial paint remover.
- Paint Stains (Oil-based). Poultice with one of the powdered poultice materials and mineral spirits. Deep stains may require methylene chloride. When using highly volatile solvents in poulticing, use a paper towel, pouring the solvent on the paper towel and then placing the towel on the stained area.
- Ink Stains. Poultice with one of the powdered poultice materials and mineral spirits or methylene chloride. When using highly volatile solvents in poulticing, use a paper towel, pouring the solvent on the paper towel and then placing the towel on the stained area.
- Biological Stains. Poultice with one of the poultice materials and dilute ammonia or bleach or hydrogen peroxide. WARNING: DO NOT MIX AMMONIA AND BLEACH! THIS COMBINATION CREATES A TOXIC GAS!
- Flammable Materials. The preceding text does not purport to address possible safety concerns associated with the use of flammable solvents. The user is directed to the manufacturer’s labeling and MSDS for further direction in the safe handling and use of these products. Commercially available cleaners exist for remedy of many of the common stains. These cleaners may have fewer health and safety concerns in some cases.
Applying The Poultice
- Prepare The Poultice. If using a powdered poultice material, mix with the cleaning agent or chemical to a paste with a thick, creamy consistency. If using paper, soak in the chemical and let drain. Don’t let the liquid drip.
- Prepare Stain Area. Wet the stained area with distilled water.
- Apply the poultice to the stained area about 1/4″ to 1/2″ thick, and extend the poultice beyond the stained area by about 1″. Use a wood or plastic scraper to spread the poultice evenly.
- Cover the poultice with plastic and tape the edges to seal it. Punch several small holes in the plastic to allow vapor to escape.
- Allow the poultice to dry thoroughly, usually about 24 to 48 hours. The drying process draws the stain out of the stone and into the poultice material. After about 24 hours, remove the plastic and allow the poultice to dry.
- Remove the poultice from the stain. Rinse with distilled water and buff dry with a soft cloth.
- Repeat the poultice application if the stain is not removed. It may take five or more applications for difficult stains.
- If the surface is etched by the chemical, apply polishing powder and buff with a polishing pad recommended by the Polishing Powder Manufacturer.
Source: Marble of Institute – Cleaning and Maintenance