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Historic Preservation - Technical Procedures

Spectitle:

Removing Efflorescence From Concrete

Procedure code:

0371016R

Source:

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

Division:

Concrete

Section:

Concrete Cleaning

Last Modified:

02/24/2012

Details:

Removing Efflorescence From Concrete



REMOVING EFFLORESCENCE 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
         efflorescence from concrete using chemical solvents.

    B.   Efflorescence is a condition where white deposits form on
         the surface of the concrete.  These deposits often
         contain calcium, sodium and potassium hydroxides or
         carbonates, bicarbonates, chlorides and sulfates of
         calcium and magnesium.  

    C.   The surface deposits may originate as soluble compounds
         within the concrete or in the soil.  These compounds
         combined with the presence of water gradually migrate in
         solution to the wall surface, where they remain when the
         water evaporates.  Surface deposits may also result from
         acid etching with hydrochloric acid, sometimes used to
         roughen the concrete surface.

    D.   Surface deposits originating from within the concrete are
         usually soluble and may be removed by scrubbing with
         water alone or hosing with water under high pressure.  

    E.   Surface deposits composed mainly of calcium acid
         carbonate and magnesium acid carbonate from the soil or
         calcium hydroxide should be washed off as soon as
         possible using water alone.  These deposits are water-soluble
         for only a brief period of time after reaching
         the atmosphere, when carbon dioxide converts them to
         water-insoluble calcium carbonate and magnesium
         carbonate, which are impossible to remove without the use
         of acids.

    F.   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.

    G.   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.   Use one of the following solvents (see Section 3.02 A.
         below for mixing proportions):

         Acetic Acid (C2H4O2):

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

         2.   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.)

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

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

         -OR-

         Hydrochloric Acid (30-35%):

         1.   A strong corrosive irritating acid.

         2.   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*.

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

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

         -OR-

         Phosphoric Acid (H3PO4):

         1.   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.

         2.   Other chemical or common names include
              Orthophosphoric acid.

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

         4.   Available from chemical supply house or hardware
              store.

    B.   Calcium Hydroxide:

         1.   Other chemical or common names include Calcium
              hydrate*; Hydrated lime*; Lime hydrate*; Slaked
              lime*.

         2.   Potential Hazards:  SKIN IRRITANT, AVOID INHALATION
              OF THE DRY POWDER.

         3.   Available from chemical supply house, construction
              materials yard, construction specialties
              distributor, garden and lawn supply center, or
              hardware store.

    C.   Filler material such as paper pulp

    D.   Mineral water

    E.   Plastic sheeting

    F.   Clean dry towels for blotting the area after treatment

    G.   Masking tape

    H.   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.   Glass or ceramic container for mixing the poultice
         solution

    B.   Rubber of plastic pale for mixing the acid and water
         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.   Mix in a glass or ceramic bowl one of the following:

         1 part hydrochloric acid in 9 to 19 parts water, OR

         1 part phosphoric acid in 9 parts water, OR

         1 part phosphoric acid plus 1 part acetic acid in 19
         parts water.

         CAUTION:  ACID IS ALWAYS ADDED TO WATER; NEVER ADD WATER
         TO CONCENTRATED ACID BECAUSE THE WATER CAN BECOME
         SUPER-HEATED AND TURN TO STEAM, SPLASHING ACID ON THE USER.

    B.   Saturate the concrete with clean, clear water.

    C.   Begin by using the first mixture listed above and apply
         to the affected concrete surface with a stiff, non-metallic bristle brush.

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

    E.   If the first mixture is unsuccessful in adequately
         removing the efflorescence, repeat the treatment using
         the other mixtures listed in the order displayed until
         successful results are achieved.  

    F.   For concrete heavily laden with potential efflorescence:

         1.   Remove all visible surface salts following A-E
              directly above.  

         2.   Follow by applying a poultice of paper pulp
              saturated in water and allow to dry.

         3.   Remove the dried poultice using a wood or plastic
              spatula.

         4.   Thoroughly rinse the surface with clean, clear
              water and allow to dry.

         5.   Repeat as necessary to achieve the desired level of
              cleanliness.

3.03 ADJUSTING/CLEANING

    A.   At the end of the job, if there is a supply of dilute
         acid to be disposed of, neutralize it by stirring in 3
         pounds of powdered calcium hydroxide for every gallon of
         the dilute (1-3) acid.  The resulting solution is a
         harmless mixture of calcium hydroxide and calcium
         fluoride.

                         END OF SECTION