Removing Coal Tar Stains from Concrete

PREFACE

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

1. This specification provides guidance on removing several types of 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: likely to penetrate deeply.

2. Safety Precautions:

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

   2. DO NOT store any chemicals in unmarked containers.

   3. The manufactured treatments if used should follow the manufacturer’s guidance on product use for safety.

   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.

3. Read “General Project Guidelines” along with this specification. 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). The 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)

4. See also “Removing Asphalt Stains from Concrete”.

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 (*).

1. Aerosol freezing agent or ice.

2. For hot-applied coal tar: scouring powder.

3. For cutback coal tar:

   1. A commercial product produced for the removal of coal tar stains such as “Sure Klean Asphalt and Tar Remover” (ProSoCo, Inc.) or approved equal.

   2. Filler material such as talc.

   3. Mineral water.

4. Clean dry towels for blotting the area after treatment.

5. Clean, potable water.

6. Accessible source of water, soap and towels for washing and rinsing in case of emergencies associated with the use of chemicals.

2.02 EQUIPMENT

1. For poulticing:

   1. Glass or ceramic container for mixing the solution.

   2. Wooden utensil for stirring the ingredients.

2. Wood or plastic spatula.

3. Stiff bristle brushes (non-metallic).

PART 3–EXECUTION

3.01 PREPARATION

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.

1. 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.

2. Removing Cutback Coal Tar:

3. 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. Apply a commercial product made for the removal of coal tar stain and follow manufacturer’s guidance for its use.

   3. If a brown color remains on the surface, treat the area using the procedure for removing light stains of iron rust from concrete (see “Poulticing Iron Rust Stains from Concrete” for guidance).