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Historic Preservation - Technical Procedures

Spectitle:

Removing Salts/Efflorescence From Brick And Stone Masonry

Procedure code:

0450002R

Source:

Hspg Prepared For Nps - Sero

Division:

Masonry

Section:

Masonry Restoration & Cleaning

Last Modified:

11/13/2012

Details:

Removing Salts/Efflorescence From Brick And Stone Masonry



REMOVING SALTS/EFFLORESCENCE FROM BRICK AND STONE MASONRY


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing salt
         deposits/efflorescence from brick and stone masonry.  

    B.   Efflorescence is a condition where white (salt) deposits
         form on the surface of the masonry.  The formation of
         salts is usually a sign of excessive amounts of moisture
         in the masonry.  Salt deposits on the masonry surface may
         develop from:

         1.   Soluble compounds within the masonry or in the
              soil.  

              a.   In the presence of water, these compounds
                   gradually migrate to the wall surface, where
                   they remain when the water evaporates.

              b.   These types of surface deposits are water
                   soluble and can usually be removed by washing
                   the wall with water from a garden hose
                   supplemented by scrubbing with a stiff bristle
                   brush.

         2.   Improper or insufficient rinsing of masonry after
              chemical cleaning or repointing.

         3.   The penetration of rain into the masonry through
              deteriorated mortar joints and other failures in exterior envelope (lack/failing flashing, expansion joint caulking missing, etc.).

         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 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.  However, they should be washed from
         the surface as soon as possible.  Some salt deposits are
         water-soluble for only a brief period after reaching the
         atmosphere.  Carbon dioxide in the atmosphere eventually
         converts these salts into water-insoluble carbonates,
         which are impossible to remove without the use of acids.
         
         NOTE:  THE REMOVAL OF SALT DEPOSITS USING ACID IS NOT
         DESCRIBED IN THIS PROCEDURE.

1.02 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements:

         1.   Do not do exterior wet work when the air
              temperature is below 40 degrees F.

         2.   NEVER begin cleaning when there is any likelihood
              of frost or freezing.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Clean, potable water

2.02 EQUIPMENT

    A.   Garden hose and nozzle

    B.   Stiff bristle brushes (nonmetallic)

    C.   Wood or plastic scrapers


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Before proceeding with steps to remove efflorescence,
         first decide the cause and extent of the problem 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 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. Horizontal projects such cornices and vertical elements such as parapets and chimneys are areas of potential risk.

         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.   Dry brush the surface with a stiff bristle (nonmetallic)
         brush, or wash it with clean, clear water from a garden
         hose, supplemented by scrubbing with a stiff bristle
         brush if necessary.

    B.   Remove sulfate crusts using a heavy wooden scraper.

    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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