Removing Etch Marks In Marble
- Procedure code:
- Outdoor Sculpture Manual - Center For Public Buildings
- Last Modified:
PREFACE: The cleaning or removal of stains or blemishes from stone may involve the use of liquids, detergents or solvents which may run off on adjacent material, discolor the stone or drive the stains deeper into porous stones. Use the products and techniques described here only for the combinations of problem and stone specified.
- This procedure includes guidance on removing etch marks in marble. The removal process requires two steps:
- Removal of the stain or substance causing the etch marks by applying a poultice or "nest". Either method is acceptable, and both are included in this entry.
- Re-polishing the surface once the stain is removed (see 04455-02-P "Re-polishing Marble" for re-polishing procedures).
- Etching involves alteration of the surface reflection, especially a change or reduction in the specular character or gloss of a highly polished surface.
- Etch marks are typically caused by certain acids left on the finish of stone surfaces. These blemishes can be caused by substances such as wine, beer, fruit juices, vinegar, tomato products, mustard, carbonated beverages, ink or salad dressing. Acid containing substances, such as these, will dissolve portions of the stone, particularly calcareous stones such as marble or limestone. The exposed surface below the affected areas will not be polished, but will be natural stone and therefore will appear as a non-reflective area.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).
- For additional information on poulticing, see 04455-02-R.
- For general information the characteristics, uses and problems associated with marble, see 04455-01-S.
NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).
- Common laundry bleach or a 6% solution of hydrogen peroxide as the active agent in the poultice:
- Hydrogen Peroxide (H202):
- An unstable compound used especially as an oxidizing and bleaching agent, an antiseptic, and a propellant.
- Other chemical or common names include Peroxide of hydrogen*; Solution of hydrogen dioxide*; Superoxol*; (hydrogen peroxide is commonly sold as a 3% solution; Superoxol is a 30% solution; Superoxol causes flesh burns; 3% hydrogen peroxide does not).
- Potential Hazards: Toxic (when concentrated); caustic to flesh (gasoline, kerosene and mineral spirits are each a mixture of compounds from petroleum, all of which fall within a specified range of properties); Flammable (in high concentration).
- Available from chemical supply house, drugstore, pharmaceutical supply distributor, or hardware store.
- White absorbent material (molding plaster, untreated white flour, white tissue, paper towels, powdered chalk, talc, fullers earth or laundry whiting)
- Mineral water
- Plastic sheeting
- Clean dry towels for blotting the area after treatment
- Glass or ceramic container for mixing the solution
- Wooden utensil for stirring the ingredients
- Wood or plastic spatula
- Examine the marble surface CAREFULLY to determine the cause of the problem before proceeding with any cleaning operation.
3.02 ERECTION, INSTALLATION, APPLICATION
- The Poultice Method:
- Rinse the area to be treated with mineral water.
- Pour hydrogen peroxide solution in a glass or ceramic bowl.
- Thoroughly moisten the stained surface with this liquid. Be sure to dampen well beyond the stain.
- Mix the remaining liquid with the white absorbent material to form a paste the consistency of oatmeal or cake icing. (Approximately one pound of paste is needed for every square foot of surface area to be treated.)
- Using a wooden or plastic spatula, apply the paste to the stained surface in layers no more than 1/4 inch thick. The poultice should extend well beyond the stain to prevent forcing the stain into previously clean stone.
- Check the coating for air pockets or voids.
- Cover the poultice with plastic sheeting and seal with masking tape.
- Let set for 48 hours (unless otherwise specified).
- After set period, dampen the poultice with mineral water.
- Remove the poultice with a wooden or plasticspatula to avoid scratching the surface.
- Again, thoroughly rinse the cleaned area with mineral water, blot with clean towels and allow the surface to dry.
- Once the surface has dried completely, check for remaining residue and repeat the treatment if necessary.
- The "Nest" Method:
NOTE: DO NOT USE BLEACH ON DARK COLORED STONES AS THIS WILL CAUSE THE STONE TO LIGHTEN.
- Pour a moderate amount of mineral water into the container.
- Add a small amount of molding plaster to the water.
- Stir the mixture, continue adding plaster and stirring until the solution has the consistency of toothpaste.
- Mold the paste like a bird's nest and place it on the stain. Be sure the mold covers the entire stain and parts of the unsoiled stone surrounding the entire stain.
- Allow the nest to dry (approximately 30 minutes).
- Pour some hydrogen peroxide solution into the nest and allow to set for about three hours.
- After the set period, remove the mold with a wooden scraper (to avoid scratching the surface).
- Wash the surface thoroughly with mineral water.
- Blot the surface and allow it to dry completely.
- If residual staining remains, repeat the treatment until the entire stain has been removed.
NOTE: Either method of removing etch marks should be followed by re-polishing of the stone surface (see 04455-02-P "Re-polishing Marble").