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Historic Preservation - Technical Procedures

Spectitle:

Removing Gypsum Plaster Stains From Concrete

Procedure code:

0371022R

Source:

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

Division:

Concrete

Section:

Concrete Cleaning

Last Modified:

02/24/2012

Details:

Removing Gypsum Plaster Stains From Concrete



REMOVING GYPSUM PLASTER 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 THE 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 gypsum
         plaster stains from concrete using hydrochloric acid and
         detergent.

    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 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.   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.

    B.   Detergent

2.02 EQUIPMENT

    A.   Wood or plastic scraper

    B.   Stiff bristle brush (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
    WASHED AWAY.

    A.   Scrape off all blobs and masses; then scrub with cold or
         luke-warm (not hot) water and detergent.

    B.   If this is not effective, apply a solution of 1 part
         hydrochloric acid in 19 parts water and scrub with a
         stiff (non-metallic) bristle brush.

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

    D.   Repeat the process as necessary to achieve the desired
         level of cleanliness.

                         END OF SECTION