Removing Gypsum Plaster Stains From Concrete
- Procedure code:
- Hstrc Concrete: Investigation & Rpr/Pre-Conf Training - 1989
- Concrete Cleaning
- Last Modified:
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
A. This procedure includes guidance on removing gypsum
plaster stains from concrete using hydrochloric acid and
B. Safety Precautions:
1. DO NOT save unused portions of stain-removal
2. DO NOT store any chemicals in unmarked containers.
3. EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY
SOLVENT IS USED. USE RESPIRATORS WITH SOLVENT
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).
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,
4. Available from chemical supply house, drugstore or
pharmaceutical supply distributor, or hardware
A. Wood or plastic scraper
B. Stiff bristle brush (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. 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