Removing Efflorescence From Marble
- Procedure code:
- Stain Removal Guide For Stone - F. M. Hueston
- Last Modified:
REMOVING EFFLORESCENCE FROM MARBLE
THE CLEANING OR REMOVAL OF STAINS FROM STONE MAY INVOLVE THE USE OF
LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON ADJACENT
MATERIAL, DISCOLOR THE STONE OR DRIVE THE STAINS DEEPER INTO POROUS
STONES. USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY FOR
THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.
A. This procedure includes guidance on removing
efflorescence from marble surfaces. The variety of efflorescence or salt stains include among others:
1. sulfates of sodium, potassium, magnesium, or calcium;
2. nitrates of sodium, potassium, and calcium;
3. calcium carbonate;
4. sodium chloride;
B. Efflorescence is a condition where white (salt) deposits
form on the surface of the marble. The formation of
salts is usually a sign of excessive amounts of moisture
in the stone masonry. Salt deposits on the stone
surface may develop from:
1. Soluble compounds within the marble or in the soil.
In the presence of water, these compounds gradually
migrate to the wall surface, where they remain when
the water evaporates.
2. Improper or insufficient rinsing of stone masonry
after chemical cleaning or repointing.
3. The penetration of rain into the stone masonry
through deteriorated mortar joints.
4. Exposure to air pollution, which can result in the
formation of thick sulfate (salt) crusts on the
underside of moldings and eaves, areas not
regularly washed by rainfall.
5. Capillary movement of moisture through stone
masonry, the drying out of walls associated with a
damp proofing treatment or the elimination of a
ground water source may increase the amount of salt
at or near the wall surface.
C. These deposits are generally not harmful to the building,
But, the mitgration of dissolved salts into the mortar joints could result in damage with salt crystals forming and expanding.
The source of the water that carries the dissolved salts should be determined and abated before attempting to remove the staining.
D. 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).
E. For general information on the characteristics, uses and
problems associated with marble, see 04455-01-S.
A. Dry, white, cotton cloths
B. Stainless steel wool (000)
A. Wood or plastic spatula
B. Stiff, fiber bristle brush
A. Examine the marble surface CAREFULLY to determine the
cause of staining before proceeding with any cleaning
operation. Look for potential sources of moisture and
make repairs as required:
1. Determine the age of the structure: Efflorescence
on older buildings is typically caused by the
presence of soluble salts in the construction
combined with moisture.
2. Determine the location of the efflorescence:
Examination may show where the water is entering.
a. Are the salt crystals accumulating on the
joints or on the units?
b. Can any changes in the wall composition or in
the adjacent surroundings be recognized that
might show the source of the problem?
3. Examine the condition of the stone masonry:
a. CAREFULLY EXAMINE the wall for open gaps or
cracks in joints and around openings that
could allow water to enter the building.
1) Are joints properly caulked or sealed?
2) Are flashings and drips in good
3) Are there open or eroded mortar joints in
copings or in sills?
b. Carefully note the condition and profile of
the mortar joints.
c. Repair cracks in masonry and/or repoint as
necessary before proceeding with the cleaning
4. Examine wall sections and details of construction:
Carefully examine roof and wall junctures and
flashing details for possible sources of moisture
5. Examine laboratory test reports on the materials:
The problem may stem from the composition or misuse
of the material.
3.02 ERECTION, INSTALLATION, APPLICATION
A. Carefully remove any surface deposits using a soft cloth
B. If necessary, gently buff the surface using a stiff
fiber bristle brush or 000 steel wool.
C. Remove sulfate crusts using a heavy wooden scraper.
D. Wipe the surface again with a clean, soft cloth.
E. If the efflorescence reappears, repeat the process. It
may take several months to eliminate the problem once the
source of excess moisture has been controlled.
C. If efflorescence is a persistent problem, it may be
necessary to reduce the level of soluble salts present
within the masonry. Two methods of masonry desalination
are described in 04500-03-R. Refer to this procedure for