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Historic Preservation - Technical Procedures

Spectitle:

Removing Finishing And Curing Discolorations From Concrete

Procedure code:

0371018R

Source:

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

Division:

Concrete

Section:

Concrete Cleaning

Last Modified:

02/24/2012

Details:

Removing Finishing And Curing Discolorations From Concrete



REMOVING FINISHING AND CURING DISCOLORATIONS 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
         discolorations from concrete that develop during the
         finishing and curing operations.  Guidance is provided
         for removing the following types of discoloration:

         1.   Dark discoloration,

         2.   Light discoloration, and

         3.   Mottling.

    B.   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.

    C.   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 MANUFACTURERS

    A.   The Procter & Gamble Co.
         P.O. Box 599
         Cincinnati, OH  45202
         513/983-1100

2.02 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 Dark Discolorations:

         1.   Hydrochloric Acid (30-35%):

              a.   A strong corrosive irritating acid.

              b.   Other chemical or common names include
                   Chlorhydric acid; Hydrogen chloride; Muriatic
                   acid* (generally available in 18 degree and 20
                   degree Baume solutions); Marine acid*; Spirit
                   of salt*; Spirit of sea salt*.

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

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

              -OR-

              Diammonium Citrate:

              a.   Other chemical or common names include
                   Ammonium citrate; Ammonium citrate secondary.

              b.   Potential Hazards:  CORROSIVE TO CONCRETE,
                   STEEL, WOOD OR GLASS.

              c.   Available from chemical supply house,
                   drugstore or pharmaceutical supply
                   distributor.

         2.   Clean, potable water

    B.   For Light Discolorations:

         1.   Neutral detergent such as "Orvis" (Procter and
              Gamble), or approved equal, using dilution as
              determined by tests on material to be cleaned.

         2.   Clean, potable water

         -OR-

         1.   Acetic Acid:  

              a.   A colorless pungent liquid acid that is the
                   chief acid of vinegar and that is used
                   especially in synthesis (as of plastics).

              b.   Other chemical or common names include Vinegar
                   acid*.  (Vinegar itself, which contains about
                   4% acetic acid, may be suitable for some
                   purposes requiring acetic acid.)

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

              d.   Available from chemical supply house (both
                   commercial and scientific), drugstore or
                   pharmaceutical supply distributor, grocery
                   store or supermarket, or hardware store.

         2.   Vinegar:

              a.   Potential Hazards:  CORROSIVE TO CONCRETE,
                   STEEL, WOOD OR GLASS.

              b.   Available from grocery store or supermarket.

              c.   Vinegar itself, which contains about 4% acetic
                   acid, may be suitable for some purposes
                   requiring acetic acid.

         3.   Phosphoric Acid:

              a.   A syrupy or deliquescent tribasic acid used
                   especially in preparing phosphates (as for
                   fertilizers), in rust-proofing metals, and as
                   a flavoring in soft drinks.

              b.   Other chemical or common names include
                   Orthophosphoric acid.

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

              d.   Available from chemical supply house or
                   hardware store.

         4.   Clean, potable water

    C.   For Mottling (light spots):

         1.   Sodium Hydroxide (NaOH):

              a.   A white brittle solid that is a strong caustic
                   base used especially in making soap, rayon,
                   and paper.

              b.   Other chemical or common names include Caustic
                   soda*; Hydrate of soda*; Hydrated oxide of
                   sodium*; Lye*; Mineral alkali*; Soda lye*; Sodic
                   hydrate*; Sodium hydrate*.

              c.   Potential Hazards:  CORROSIVE TO FLESH AND
                   FLAMMABLE (WHEN IN CONTACT WITH ORGANIC
                   SOLVENTS).

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

         2.   Clean, potable water

2.03 EQUIPMENT

    A.   Stiff, bristle brushes (non-metallic)


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
    THOROUGHLY WASHED AWAY.

    A.   For Removing Dark Discolorations:

         1.   If discovered early, dark discoloration caused by
              inadequate curing can sometimes be overcome by
              washing for a half hour at a time with hot water,
              allowing to dry, and repeating as necessary.

         2.   Dark discolorations caused by trowel burns are more
              difficult to remove.

              a.   Apply a solution of 1 part hydrochloric acid
                   in 49 to 99 parts of water -OR- a solution of
                   25 to 35 ounces by weight of diammonium
                   citrate in 1 gallon of water.

              b.   Scrub the solution on using a stiff non-metallic bristle brush.  
                    A white gel will form in the process.  Dilute with water and
                   continuously agitate during the treatment to
                   avoid having it bond tightly to the concrete.

              c.   Rinse the gel off with clean, clear water and
                   allow to dry.  It may be necessary to treat
                   the concrete two or three more times.  It also
                   helps if the concrete is cured with water
                   between treatments.

    B.   For Removing Light (White) Discolorations:

         1.   Non-acidic treatments should be tried first, using
              water and a neutral detergent.

         2.   If this is insufficient, apply a solution of 1 part
              acetic acid in 19 parts water, undiluted vinegar,
              and 1 part phosphoric acid in 19 parts water.

         3.   Rinse with clean, clear water and allow to dry.

         4.   Repeat the process as necessary.

    C.   For Removing Mottling (Light Spots):

         1.   Apply a solution of 12 ounces of sodium hydroxide
              by weight in 1 gallon of water.

         2.   Leave on the surface for 24 hours.

         3.   Rinse the surface thoroughly with clean, clear
              water and allow to dry.

         4.   Repeat the process as necessary.

                         END OF SECTION