REMOVING ETCH MARKS IN MARBLE


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.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing etch marks
         in marble.  The removal process requires two steps:

         1.   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.

         2.   Repolishing the surface once the stain is removed
              (see 04455-02-P "Repolishing Marble" for
              repolishing procedures).

    B.   Etching involves alteration of the surface reflection,
         especially a change or reduction in the specular
         character or gloss of a highly polished surface.  

    C.   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.

    D.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   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).

    E.   For additional information on poulticing, see 04455-02-R.

    F.   For general information the characteristics, uses and
         problems associated with marble, see 04455-01-S.


PART 2---PRODUCTS

2.01 MATERIALS

    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 (*).

    A.   Common laundry bleach or a 6% solution of hydrogen
         peroxide as the active agent in the poultice:

         Hydrogen Peroxide (H202):

         1.   An unstable compound used especially as an
              oxidizing and bleaching agent, an antiseptic, and a
              propellant.

         2.   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).

         3.   Potential Hazards:  TOXIC (when concentrated);
              CORROSIVE 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).

         4.   Available from chemical supply house, drugstore,
              pharmaceutical supply distributor, or hardware
              store.

    B.   White absorbent material (molding plaster, untreated
         white flour, white tissue, paper towels, powdered chalk,
         talc, fullers earth or laundry whiting)

    C.   Mineral water

    D.   Plastic sheeting

    E.   Clean dry towels for blotting the area after treatment

2.02 EQUIPMENT

    A.   Glass or ceramic container for mixing the solution

    B.   Wooden utensil for stirring the ingredients

    C.   Wood or plastic spatula


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Examine the marble surface CAREFULLY to determine the
         cause of the problem before proceeding with any cleaning
         operation.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   The Poultice Method:

         NOTE:  DO NOT USE BLEACH ON DARK COLORED STONES AS THIS
         WILL CAUSE THE STONE TO LIGHTEN.

         1.   Rinse the area to be treated with mineral water.

         2.   Pour hydrogen peroxide solution in a glass or
              ceramic bowl.

         3.   Thoroughly moisten the stained surface with this
              liquid.  Be sure to dampen well beyond the stain.

         4.   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.)

         5.   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.

         6.   Check the coating for air pockets or voids.

         7.   Cover the poultice with plastic sheeting and seal
              with masking tape.

         8.   Let set for 48 hours (unless otherwise specified).

         9.   After set period, dampen the poultice with mineral
              water.

         10.  Remove the poultice with a wooden or plastic
              spatula to avoid scratching the surface.

         11.  Again, thoroughly rinse the cleaned area with
              mineral water, blot with clean towels and allow the
              surface to dry.

         12.  Once the surface has dried completely, check for
              remaining residue and repeat the treatment if
              necessary.

    B.   The "Nest" Method:

         1.   Pour a moderate amount of mineral water into the
              container.

         2.   Add a small amount of molding plaster to the water.

         3.   Stir the mixture, continue adding plaster and
              stirring until the solution has the consistency of
              toothpaste.

         4.   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.

         5.   Allow the nest to dry (approximately 30 minutes).

         6.   Pour some hydrogen peroxide solution into the nest
              and allow to set for about three hours.

         7.   After the set period, remove the mold with a wooden
              scraper (to avoid scratching the surface).

         8.   Wash the surface thoroughly with mineral water.

         9.   Blot the surface and allow it to dry completely.

         10.  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 repolishing of the stone surface (see 04455-02-P
    "Repolishing Marble").

                         END OF SECTION