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Historic Preservation - Technical Procedures

Spectitle:

Removing Efflorescence From Marble

Procedure code:

0445525R

Source:

Stain Removal Guide For Stone - F. M. Hueston

Division:

Masonry

Section:

Marble

Last Modified:

07/30/2013

Details:

Removing Efflorescence From Marble



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.


PART 1---GENERAL

1.01 SUMMARY

    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;

        5. silica.

    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,
          just unattractive.   

        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

         3.   Submittals

         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.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Dry, white, cotton cloths

    B.   Stainless steel wool (000)

2.02 EQUIPMENT

    A.   Wood or plastic spatula

    B.   Stiff, fiber bristle brush


PART 3---EXECUTION

3.01 EXAMINATION

    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
                        condition?

                   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
                   operations.

         4.   Examine wall sections and details of construction:
              Carefully examine roof and wall junctures and
              flashing details for possible sources of moisture
              entry.

         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
         first.  

    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
         guidance.

                         END OF SECTION
 


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