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Historic Preservation - Technical Procedures
Removing Coal Tar Stains From Concrete
Hstrc Concrete: Investigation & Rpr/Pre-Conf Training - 1989
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.
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
2. Cutback Coal Tar: This is likely to penetrate
B. Safety Precautions:
1. DO NOT save unused portions of stain-removal
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
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
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
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.
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*;
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
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)
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
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
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
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
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