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Historic Preservation - Technical Procedures

Spectitle:
Removing Coal Tar Stains From Concrete

Procedure code:
0371012R

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

Division:
Concrete

Section:
Concrete Cleaning

Last Modified:
02/24/2012

Details:
Removing Coal Tar Stains From Concrete



REMOVING COAL TAR 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 coal tar
         such as roofing tar from concrete using freezing agents
         and poulticing.  The types of tar staining addressed here
         include the following:

         1.   Hot-Applied Coal Tar:  Like molten asphalt, this
              type of tar usually does not penetrate concrete
              deeply.

         2.   Cutback Coal Tar:  This is likely to penetrate
              deeply.

    B.   Safety Precautions:

         1.   DO NOT save unused portions of stain-removal
              materials.

         2.   DO NOT store any chemicals in unmarked containers.

         3.   THE ORGANIC SOLVENTS LISTED FOR REMOVING COAL TAR
              ARE POISONOUS, CARCINOGENIC OR FLAMMABLE.
              EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY
              SOLVENT IS USED.  USE RESPIRATORS WITH SOLVENT
              FILTERS.

              NOTE:  SOME OF THE SOLVENTS LISTED ARE KNOWN
              CARCINOGENS AND MAY BE BANNED IN SOME STATES.

         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).

    D.   For additional information related to this procedure, see
         also 03710-05-R "Removing Asphalt Stains From Concrete".

    E.   For additional information on poulticing, see 04455-02-R.


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.   Aerosol Freezing Agent or Ice

    B.   For Hot-Applied Coal Tar:

         1.   Scouring powder

    C.   For Cut-Back Coal Tar:

         1.   Benzene (C6H6):

              a.   A colorless, volatile, flammable, toxic,
                   liquid, aromatic hydrocarbon used in organic
                   synthesis, as a solvent and as a motor fuel.

              b.   Other chemical or common names include Benzol;
                   Benzole; Phene; Phenyl hydride; Coal naphtha*;
                   Motor benzol*.

              c.   Potential Hazards:  FLAMMABLE.

              d.   Available from automotive supply distributor,
                   chemical supply house, dry cleaning supply
                   distributor, hardware store or paint store.

              e.   Benzene and benzine should not be confused.
                   Benzene is a distinct chemical compound
                   obtained from coal tar.  Benzine is a mixture
                   of aromatic hydrocarbons of similar boiling
                   points derived from petroleum.

         2.   Filler material such as talc

         3.   Mineral water

    D.   Clean dry towels for blotting the area after treatment

    E.   Clean, potable water

    F.   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.   For Poulticing:

         1.   Glass or ceramic container for mixing the solution

         2.   Wooden utensil for stirring the ingredients

    B.   Wood or plastic spatula

    C.   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
    WASHED AWAY.

    A.   Removing Hot-Applied Coal Tar:

         1.   Chill the coated area with an aerosol freezing
              agent or ice and scrape or chip while the material
              is brittle.  

         2.   Using a stiff bristle brush, scrub the surface with
              scouring powder and water.

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

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

    B.   Removing Cutback Coal Tar:

         NOTE:  THIS TREATMENT MAY LEAVE A BROWN STAIN, EVEN AFTER
         SEVERAL APPLICATIONS.

         1.   Remove as much as possible by chilling with an
              aerosol freezing agent or ice and chipping (See
              3.02 A. above).

         2.   Mix a poultice of benzene and talc.  A quantity of
              talc should be used which is adequate to cover the
              affected area.  Benzene should be added to achieve
              the consistency of a thick paste.

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

         4.   Apply the mixture 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 migrates 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.

         9.   If a brown color remains on the surface, treat the
              area using the procedure for removing light stains
              of iron rust from concrete (see 03710-26-R).

                         END OF SECTION