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