Removing Old Sulphated Limewash From Masonry
- Procedure code:
- Developed For Hspg (Nps - Sero)
- Unit Masonry
- Last Modified:
REMOVING OLD SULPHATED LIMEWASH FROM MASONRY
THE CLEANING OR REMOVAL OF STAINS FROM MASONRY MAY INVOLVE THE
USE OF LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON
ADJACENT MATERIAL, DISCOLOR THE MASONRY OR DRIVE THE STAINS DEEPER
INTO THE POROUS MASONRY. USE THE PRODUCTS AND TECHNIQUES
DESCRIBED HERE ONLY FOR THE COMBINATIONS OF DIRT/STAIN AND MASONRY
A. This procedure includes guidance on removing old
sulphated limewash from masonry by poulticing with
B. IT IS VERY DIFFICULT TO REMOVE OLD SULPHATED LIMEWASH
FROM MASONRY WITHOUT CAUSING DAMAGE TO THE SURFACE BELOW.
THEREFORE, LIMEWASHES SHOULD ONLY BE REMOVED WHEN IT IS
ABSOLUTELY DESIRABLE AND SHOULD ONLY BE PERFORMED BY A
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. 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*.
2. Potential hazards: TOXIC; CORROSIVE TO FLESH;
CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS;
3. Available from chemical supply house, drugstore or
pharmaceutical supply distributor, or hardware
B. Filler for poulticing such as attapulgite or sepiolite
clay: Available from hardware store.
C. Clean, potable water
D. Plastic sheets for covering poultice
A. Wood or plastic spatula
B. Phosphor bronze or bristle brushes
C. Air abrasive tools (suction or pressure)
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 masonry even though the stain is gone.
NOTE: UNDER NO CIRCUMSTANCES ARE THESE TECHNIQUES TO BE USED
ON SCULPTURE OR IMPORTANT DETAILS.
NOTE: DO NOT TRY MORE THAN ONE TREATMENT ON A GIVEN AREA
UNLESS THE CHEMICALS USED FROM PRIOR TREATMENT HAVE BEEN
A. Soften the limewash by applying a poultice:
1. Mix attapulgite or sepiolite clay with water to
form a thick paste.
2. Thoroughly wet the area to be treated with clean,
3. Apply the poultice over the limewash using a wood
or plastic spatula and cover with plastic to keep
4. When the poultice has dried, brush or scrape it off
with a wooden scraper.
B. Break down the limewash surface by scrubbing with a
phosphor bronze or bristle brush and hot water; Hot water
should be used if the limewash has an oil or tallow
D. If residual traces remain, wet the wall again with hand
sprays and wash with a 30-35% solution of hydrochloric
E. Thoroughly rinse the surface with clean water and allow
F. Repeat as necessary to achieve the desired level of
END OF SECTION