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Historic Preservation - Technical Procedures

Spectitle:

Removing Copper/Bronze Stains From Limestone And Marble

Procedure code:

0440007R

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Stonework

Last Modified:

07/02/2012

Details:

Removing Copper/Bronze Stains From Limestone And Marble



REMOVING COPPER/BRONZE STAINS FROM LIMESTONE AND MARBLE


THE CLEANING OR REMOVAL OF STAINS FROM STONE MAY INVOLVE THE USE
OF LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON ADJACENT
MATERIAL, DISCOLOR THE MASONRY OR DRIVE THE STAINS DEEPER INTO THE
POROUS STONE.  USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY
FOR THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing copper and
         bronze stains from limestone and marble.  Several methods
         are described.

    B.   Copper stains appear as green or muddy-brown
         discolorations and result from the action of moisture on
         nearby or embedded bronze, copper and/or brass items.  

    C.   Safety Precautions:

         1.   DO NOT save unused portions of stain-removal
              materials.

         2.   DO NOT store any chemicals in unmarked containers.

         3.   EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY
              SOLVENT IS USED.  USE RESPIRATORS WITH SOLVENT
              FILTERS.

         4.   No use of organic solvents indoors should be
              allowed without substantial air movement.  Use only
              spark-proof fans near operations involving
              flammable liquids.

         5.   Provide adequate clothing and protective gear where
              the chemicals are indicated to be dangerous.

         6.   Have available antidote and accident treatment
              chemicals where noted.

    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 general information on the characteristics, uses and
         problems associated with limestone, see 04460-01-S; for
         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.   For Light-colored Stains:

         1.   Sodium Hydrogen Citrate (NaC6O7H7) - (appears like
              enlarged salt granules):

              a.   Other chemical or common names include Citrate
                   of soda*.

              b.   Available from chemical supply house, drug
                   store or pharmaceutical supply distributor.

         2.   Glycerine:

              a.   A sweet syrupy hygroscopic trihydroxy alcohol
                   usually obtained by the saponification of fats
                   and used especially as a solvent and
                   plasticizer.

              b.   Other chemical or common names include
                   Glycerol; Glyceryl hydroxide; Glycyl alcohol;
                   1,2,3-propanetriol; Propenyl alcohol.

              c.   Potential Hazards:  FLAMMABLE.

              d.   Available from chemical supply house, drug
                   store or hardware store.

         3.   Cotton-wool pads

    B.   For Sharply-outlined Stains:

         1.   Sodium Hydrogen Citrate (See 2.01 A.1. above)

         2.   Crystalline Sodium Thiosulfate - white sal or
              "hypo" of photographic fixing agent (NA2S2O3):

              a.   A hygroscopic crystalline salt used especially
                   as a photographic fixing agent and a reducing
                   or bleaching agent.

              b.   Other chemical or common names include Sodium
                   hydrosulfite; Sodium Hyposulfite; Sodium
                   subsulfite; Antichlor*; Hypo*; Hyposulfite of
                   soda*.

              c.   Potential Hazards:  TOXIC; CORROSIVE TO
                   CONCRETE, STEEL, WOOD OR GLASS.

              d.   Available from chemical supply house, dry
                   cleaning supply distributor, drugstore or
                   pharmaceutical supply distributor,
                   photographic supply distributor (not camera
                   shop), or water and sanitation supply
                   distributor.

         3.   Cotton wadding

    C.   For Poulticing:

         1.   Ammonium Chloride - salt-like substance (NH4Cl):

              a.   A white crystalline volatile salt that is used
                   in dry cells and as an expectorant.:

              b.   Other chemical or common names include
                   Ammonium hydrochloride; Chloride of Ammonia*;
                   Hydrochloride of Ammonia*; Muriate of
                   Ammonia*; Sal Ammoniac*.

              c.   Potential hazards:  TOXIC; CORROSIVE TO FLESH;
                   CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.

              d.   Available from chemical supply house, dry
                   cleaning supply distributor, drugstore or
                   pharmaceutical supply distributor, or hardware
                   store.

         2.   Ammonium Hydroxide (NH5O):

              CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE
              BLEACHES, A POISONOUS GAS WILL RESULT!  DO NOT USE
              BLEACH ON BIRD DROPPINGS.

              a.   A weakly basic compound that is formed when
                   ammonia dissolves in water and that exists
                   only in solution.

              b.   Other chemical or common names include Ammonia
                   water*; Aqua ammonia*; Household ammonia*.

              c.   Potential hazards:  TOXIC; MAY IRRITATE THE
                   EYES.

              d.   Available from chemical supply house, grocery
                   store or pharmaceutical supply distributor, or
                   hardware store.

              NOTE:  TRADITIONAL USAGE OF AMMONIA DIRECT OR IN A
              PASTE WITH WHITING IS ONLY SUCCESSFUL ON LIGHT
              STAINING.

         3.   Ethylene diamine-tetra-acetic acid (EDTA):

              a.   EDTA is chelating agent used to remove
                   metallic stains from masonry.

              b.   Chelating agents are molecules that coordinate
                   metal ions together.  The metal ions in the
                   stain attach themselves to the chelating agent
                   to form either a soluble or insoluble metal
                   complex that can then be removed.

              c.   Available from chemical supply house.

              d.   It is available as an acid or in the form of
                   its more soluble sodium salts.  It is known to
                   be used as a preservative.  Its most important
                   use, however, is in the removal of unwanted
                   metal ions from water, as in the manufacturing
                   of agricultural chemical sprays.

         4.   Appropriate filler such as Attapulgite clay, talc,
              diatomite, or ground or powdered chalk

    D.   Mineral water

    E.   Distilled water

    F.   Accessible source of clean, potable water, soap and
         towels for washing and rinsing in case of emergencies
         associated with the use of chemicals

2.02 EQUIPMENT

    A.   Glass or ceramic container for mixing the solution

    B.   Bowl for mixing chalk paste

    C.   Wooden utensil for stirring the ingredients

    D.   Wood scrapers or plastic spatula

    E.   Plastic sheets

    F.   Clean dry towels for blotting the area after treatment

    G.   Masking tape

    H.   Rubber gloves to prevent skin irritation

    I.   Glass plates to cover pads

    J.   Weights


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Examine the masonry surface CAREFULLY to determine the
         cause of staining to ensure the required treatment is determined before proceeding with any          cleaning operation.

3.02 PREPARATION

    A.   Protection:  Provide adequate wash solutions (i.e. water,
         soap and towels) before starting the job.

    B.   Surface Preparation:  If possible, remove the sources of
         moisture to prevent further oxidation of the metal.
         Where the source of the stain is an embedded
         anchor, tie, or other device, the only non-destructive remedy is to
         eliminate the moisture at its source.
         
3.03 ERECTION/INSTALLATION/APPLICATION

    NOTE:  DO NOT TRY MORE THAN ONE TREATMENT ON A GIVEN AREA
    UNLESS THE CHEMICALS USED FROM PRIOR TREATMENT HAVE BEEN
    WASHED AWAY.

    A.   For Light-Colored Stains:  Apply an active agent with
         cotton-wool pads:

         1.   Thoroughly cleanse the area to be treated with
              mineral water.

         2.   Put on the rubber gloves to avoid contact with the
              chemicals to be used and to avoid unnecessary skin
              irritation.

         3.   Prepare a 15% aqueous solution of sodium hydrogen
              citrate with some glycerine (to deter evaporation)
              in the appropriate container.

         4.   Dampen the cotton-wool pads in the solution and
              apply them to the area to be treated.

         5.   Cover the pads with the glass plates.

         6.   Apply weights on top of the glass plates to insure
              close contact between the pads and the stained
              stone.

         7.   Allow the pads to set 3-4 days, before removing
              them.

         8.   Remove all the equipment including the pads,
              thoroughly rinse with mineral water and allow to
              dry.

         9.   If there is residual staining, repeat the process
              to achieve the desired level of cleanliness.

    B.   For Sharply-outlined Stains:  Apply an active agent with
         cotton wadding:

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

         2.   Put on the rubber gloves to avoid unnecessary skin
              irritation.

         3.   Mix a 15% aqueous solution of sodium hydrogen
              citrate in the glass or ceramic container.

         4.   Form a paste of ground chalk and distilled water.

         5.   Soak the cotton wadding in the sodium hydrogen
              citrate solution and apply them to the stained
              area.

         6.   Spread the chalk paste over the cotton wadding.

         7.   Sprinkle the crystalline sodium thiosulfate over
              the paste.

         8.   Allow the chemicals to act on the stain for one
              hour.

         9.   Remove all of the materials with a wood or plastic
              spatula.

         10.  Thoroughly cleanse the area with mineral water and
              allow to dry.

         11.  If there is residual staining, repeat the process
              to achieve the desired level of cleanliness.

    -OR-

    C.   Apply a poultice of ammonium chloride, ammonium
         hydroxide, EDTA, and attapulgite clay (see also 04455-02-R
         for additional guidance on poulticing).

         1.   Prepare the poultice mixture:

              a.   Add 70 g of ammonium chloride to 570 ml of
                   ammonium hydroxide; Add water to make the
                   volume 1 liter.

              b.   Add 37 g of EDTA to the ammonia water.

              c.   Add attapulgite clay to form a soft paste.

         2.   Pre-wet the stain with clean water to prevent too
              deep a penetration of the chemical cleaning agent.

         3.   Apply the poultice mixture to the stained surface
              in layers no more than 1/4 inch thick.

         4.   Cover the poultice with sheets of plastic taped
              against the wall in order to prevent too quick of
              an evaporation.

         5.   Re-wet the poultice as needed and leave to dry for
              several days.

         6.   When the paste has dried, remove it with a wood or
              plastic spatula.

         7.   Thoroughly rinse the area with clean, clear water
              in order to remove any chemical residue and allow
              to dry.

         8.   Repeat this process as often as necessary to
              satisfactorily lift or lighten the stain.

                         END OF SECTION
 


copper stains, bronze stains, copper stains on limestone, copper stains on marble, bronze stains on limestone, bronze stains on marble