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Historic Preservation - Technical Procedures
Removing Mildew Stains From Concrete
Hstrc Concrete: Investigation & Rpr/Pre-Conf Training - 1989
Removing Mildew Stains From Concrete
REMOVING MILDEW 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 mildew
stains from concrete using chemical solvents.
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. Sodium Hypochlorite (NaOCl):
1. An unstable salt produced usually in aqueous
solution and used as a bleaching and disinfecting
2. Other chemical or common names include Bleaching
solution*; Household bleach*; Laundry bleach*;
Solution of chlorinated soda*.
3. Potential Hazards: CORROSIVE TO FLESH.
4. Available from chemical supply house, grocery store
or supermarket, hardware store or janitorial supply
B. Sodium Orthophosphate:
1. Other chemical or common names include Tribasic
sodium phosphate; Trisodium orthophosphate;
Trisodium phosphate; TSP*; Phosphate of soda*.
2. Potential Hazards: CORROSIVE TO FLESH.
3. Available from chemical supply distributor,
supermarket, grocery, or hardware store.
C. Laundry detergent
D. Clean, potable water
E. Accessible source of water, soap and towels for washing
and rinsing in case of emergencies associated with the
use of chemicals
A. 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. Mix together 1 ounce by weight of powdered laundry
detergent, 1 ounce by weight of sodium orthophosphate, 1
quart of commercial sodium hypochlorite solution (which
contains about 5% sodium hypochlorite) and 3 quarts of
B. Brush apply the solution to the stained area, and allow
to sit for a few days.
C. Thoroughly rinse the surface with clean, clear water
while scrubbing with a stiff bristle brush.
CAUTION: SODIUM HYPOCHLORITE SOLUTION BLEACHES COLOR
CLOTHING AND MAY CORRODE METALS.
END OF SECTION