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Historic Preservation - Technical Procedures

Spectitle:

Poulticing Iron Rust Stains From Concrete

Procedure code:

0371026R

Source:

Hstrc Concrete: Investigation & Rpr/Pre-Conf Training - 1989

Division:

Concrete

Section:

Concrete Cleaning

Last Modified:

02/24/2012

Details:

Poulticing Iron Rust Stains From Concrete



POULTICING IRON RUST STAINS FROM CONCRETE


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


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing both surface
         and penetrating rust stains from concrete by poulticing
         with chemical solvents.

    B.   Stains of a rust color on concrete are usually caused by
         rusting of steel in or on concrete, from use of curing
         water that contains iron in solution or from pyrites
         (iron sulfide particles) occasionally found in aggregate.

    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).


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 Shallow Stains:

         1.   Oxalic Acid (COOH)2 or (H2C2O4):

              a.   A poisonous strong acid that occurs in various
                   plants as oxalates and is used especially as a
                   bleaching or cleaning agent and in making
                   dyes.

              b.   Other chemical or common names include
                   Ethanedioic acid.

              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, hardware
                   store, or photographic supply distributor (not
                   camera shop).  (Often sold under a
                   manufacturer's brand name; the chemical name
                   may appear on the label.)

         2.   Ammonium Hydrogen Fluoride:  USE EXTREME CAUTION
              WITH THIS MATERIAL.

              a.   Other chemical or common names include Acid
                   Ammonium fluoride; Ammonium bifluoride.

              b.   Potential Hazards:  TOXIC; CORROSIVE TO FLESH;
                   CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS;
                   FLAMMABLE.

              c.   Available from chemical supply house or dairy
                   supply distributor.

              d.   USE EXTREME CAUTION WITH THIS MATERIAL.

    B.   For Deep Penetrating Stains:

         1.   Sodium Citrate (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.   Glycerol:

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

              b.   Potential Hazards:  FLAMMABLE.

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

         3.   Hydrogen Peroxide (H202):

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

              b.   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).

              c.   Potential Hazards:  TOXIC (when concentrated);
                   CORROSIVE TO FLESH; FLAMMABLE (in high
                   concentration).

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

         4.   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.

    C.   Soap Powder

    D.   Filler material such as diatomaceous earth, talc or
         cotton wadding

    E.   Mineral water

    F.   Plastic sheeting

    G.   Clean dry towels for blotting the area after treatment

    H.   Masking tape

    I.   Clean, potable water

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

2.02 EQUIPMENT

    A.   Stiff bristle brushes (non-metallic)

    B.   Glass or ceramic container for mixing the solution

    C.   Wooden utensil for stirring the ingredients

    D.   Wood or plastic spatula


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

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

         2.   Whenever acid is used, the surface should be
              thoroughly rinsed with water as soon as its action
              has been adequate.  Otherwise it will continue
              etching the concrete even though the stain is gone.

3.02 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 Surface Stains:

         1.   Mix 1 pound oxalic acid in 1 gallon of water.
              CAUTION:  OXALIC ACID IS TOXIC.  OBSERVE WARNINGS
              ON THE LABEL.

         2.   Swab the stained area with the solution.

         3.   To quicken the stain removal action, add 1/2 pound
              of ammonium acid fluoride to the solution.
              CAUTION:  AMMONIUM ACID FLUORIDE GENERATES
              HYDROFLUORIC ACID, WHICH IS HIGHLY AGGRESSIVE AND
              TOXIC TO SKIN, EYES AND MUCOUS MEMBRANES.  THE
              EFFECTS ARE FAIRLY LONGLASTING, SO THIS COMPOUND
              SHOULD BE HANDLED WITH EVEN MORE CARE THAN MOST
              MINERAL ACIDS.

         4.   Allow the solution to sit on the stained concrete
              for 2 or 3 hours.

         5.   Thoroughly rinse the surface by scrubbing with a
              stiff bristle brush and clean, clear water.

         6.   Repeat the treatment as necessary to achieve the
              desired level of cleanliness.

    B.   For Deep Penetrating Stains:

         1.   Dissolve 11 ounces by weight of sodium citrate in 2
              quarts of lukewarm water and add 2 quarts and 12
              ounces of glycerol.

         2.   Mix the solvent solution above with diatomaceous
              earth or talc to form a thick paste having the
              consistency of oatmeal.

         3.   Thoroughly wet the concrete surface to be treated
              with clean, clear water.

         4.   Apply the poultice to the stained area using a wood
              or plastic spatula and allow to dry.  Be sure to
              spread the poultice well beyond the stained area.
              The liquid portion of the paste will migrate into
              the concrete where it will dissolve some of the
              staining material.  Then the liquid will gradually
              move back beyond the concrete surface and into the
              poultice, where it will evaporate, leaving the
              dissolved staining material in the poultice.

         5.   When the poultice has dried, brush or scrape it off
              with a wooden scraper.  

         6.   Using a stiff bristle brush, scrub the surface with
              scouring powder and clean water to remove any
              residual staining.

         7.   Thoroughly rinse the area with clean, clear water
              and allow to dry.

         8.   Repeat the process as necessary to sufficiently
              remove the stain.

         -OR-

         NOTE:  THIS METHOD REQUIRES GOOD VENTILATION TO REMOVE
         THE ACRID FUMES OF SULFUR DIOXIDE GIVEN OFF.

         1.   Dissolve 22 ounces by weight of sodium citrate in 1
              gallon of lukewarm water.

         2.   Saturate a bandage of cotton wadding in the solvent
              solution and apply the bandage for 30 minutes, or
              brush the solution on the surface every 5 or 10
              minutes.

         3.   For stains on horizontal surfaces:

              a.   Sprinkle a thin layer of sodium thiosulfate
                   over the surface and moisten it with a light
                   mist of water from a spray nozzle.  

              b.   Cover the treated area with a poultice made
                   with diatomaceous earth or talc moistened with
                   water.

         4.   For stains on vertical surfaces:

              a.   Place a poultice of diatomaceous earth or talc
                   mixed with water on a trowel.

              b.   Sprinkle sodium thiosulfate crystals on the
                   poultice and moisten slightly.

              c.   Trowel the poultice mixture onto the surface
                   so that the crystals are in direct contact
                   with the stained surface.

              NOTE:  If the thiosulfate crystals turn the brown
              stains to black, brush apply a diluted solution of
              hydrogen peroxide to the stained area and repeat
              the thiosulfate treatment.

         5.   After 1 hour, remove the poultice.  Repeat the
              treatment with fresh materials as necessary to
              achieve the desired level of cleanliness.

         6.   Scrub the surface thoroughly with clean, clear
              water and apply another treatment of the sodium
              citrate solution to prevent the stain from coming
              back.

                         END OF SECTION