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Historic Preservation - Technical Procedures

Spectitle:

Removing Soluble Salts From Within Brick And Stone Masonry

Procedure code:

0450003R

Source:

Hspg Prepared For Nps - Sero

Division:

Masonry

Section:

Masonry Restoration & Cleaning

Last Modified:

02/24/2012

Details:

Removing Soluble Salts From Within Brick And Stone Masonry



REMOVING SOLUBLE SALTS FROM WITHIN BRICK AND STONE 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 POROUS MASONRY.  USE THE PRODUCTS AND TECHNIQUES DESCRIBED
HERE ONLY FOR THE COMBINATIONS OF DIRT/STAIN AND MASONRY SPECIFIED.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing soluble
         salts from within brick and stone masonry.  Two methods
         of salt removal - or desalination - are described and
         include the application of a clay poultice and the
         application of a sand:lime render.

    B.   Reducing the salt content of masonry may be necessary if
         effloresence (salt deposits) on the surface becomes a
         persistent problem.

    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

         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).


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Clean natural fiber rags

    B.   Poulticing Materials:

         1.   Filler material for poultice:  Use absorbent clay
              or diatomaceous earth (attapulgite or sepiolite
              clay).

              a.   Available from chemical supply house (both
                   commercial and scientific), or swimming pool
                   supply distributors.

         2.   Distilled water

    C.   Sacrificial Render Materials:  

         1.   Lime putty

         2.   Sand

    D.   Clean, potable water

2.02 EQUIPMENT

    A.   Plastic sheeting

    B.   Poultice Equipment:  

         1.   Plasterer's float or broad trowel

         2.   Galvanized wire mesh

         3.   Galvanized staples

         4.   Pliers

         5.   Plastic sacks

    C.   Sacrificial Render Equipment:  

         1.   Mesh screens

         2.   Plasterer's float or broad trowel

         3.   Hacksaw blade


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Applying a Clay Poultice:

         NOTE:  THIS METHOD OF DESALINATION IS SUITED FOR USE ON
         LARGE AREAS OF MASONRY WITH MINIMAL DETAILING, OR ON
         SIMPLE MASONRY DETAILS.  FOR DELICATE DETAILS OR HIGHLY
         DAMAGED AREAS, THIS METHOD SHOULD BE PERFORMED BY A
         TRAINED CONSERVATOR.

         CAUTION:  THIS METHOD IS NOT SUITABLE FOR USE WHERE PRE-
        WETTING THE SURFACE CAN ADVERSELY AFFECT PLASTER, PAINT,
         OR EMBEDDED WOOD OR METAL.

         1.   Saturate the wall for several days by spraying with
              mists of clean, clear water.  

              a.   Mist the water evenly over the masonry surface
                   at 18 gallons per hour from fine spray heads
                   mounted to a boom.  

              b.   The length of time it takes to fully saturate
                   the wall will depend on the type of masonry,
                   and its porosity (typically 72 hours).

              CAUTION:  BE SURE TO COLLECT WATER RUN-OFF AND
              DRAIN SAFELY AWAY FROM THE BUILDING DURING THE
              CLEANING PROCESS.

         2.   When the wall is thoroughly saturated, mix filler
              material with enough distilled water to form a
              soft, sticky paste.  Mix by hand or use a small
              mechanical mixer.  BE SURE TO ADD THE CLAY TO THE
              WATER, NOT THE REVERSE.  ADDING WATER TO THE CLAY
              WILL RESULT IN A LUMPY, UNWORKABLE MIX.

         3.   Apply the poultice to the saturated wall in a
              single layer (no more than 1 inch thick) using a
              plasterer's float or broad trowel.

              NOTE:  MAKE SURE THE WALL IS THOROUGHLY SATURATED
              BEFORE APPLYING THE POULTICE TO AVOID
              REDISTRIBUTING THE SALTS BACK INTO THE MASONRY.  

         4.   To help bond the clay to the wall surface, press a
              light-gauge galvanized wire mesh into the poultice
              and tack it carefully into joints with galvanized
              staples.

         5.   Protect the treated area from direct sun or rain
              with tarpaulins as needed.

         6.   Allow the poultice to remain in place about 1
              month.  As the poultice dries, the clay will
              eventually lighten in color, crack, shrink and
              detach from the wall.

         7.   Remove the staples using pliers and roll up the
              clay and wire mesh.

         8.   Discard materials safely from the site.

         9.   Thoroughly rinse the treated area with clean, clear
              water and allow to dry.

         10.  Repeat the cycle of wetting and poulticing as
              needed to reduce the salts to an acceptable level;
              Repointing may be required at the end of the
              desalination treatment.

              -OR-

    B.   Applying a Sand:Lime Sacrificial Render:

         NOTE:  THIS IS A FAIRLY SLOW METHOD OF MASONRY
         DESALINATION AND MAY TAKE AS LONG AS SEVERAL MONTHS TO
         PRODUCE EFFECTIVE RESULTS.

         NOTE:  THIS METHOD IS SUITED FOR USE ON LARGE AREAS OF
         MASONRY WITH MINIMAL DETAILING, OR ON SIMPLE MASONRY
         DETAILS.  FOR DELICATE DETAILS OR HIGHLY DAMAGED AREAS,
         THIS METHOD SHOULD BE PERFORMED BY A TRAINED CONSERVATOR.

         CAUTION:  THIS METHOD IS NOT SUITABLE FOR USE WHERE PRE-
        WETTING THE SURFACE CAN ADVERSELY AFFECT PLASTER, PAINT,
         OR EMBEDDED WOOD OR METAL.

         1.   Thoroughly saturate the wall with clean, clear
              water.

         2.   Mix 1 part slaked and screened lime putty with 4
              parts fine sand.

         3.   Apply the sacrificial render at least 1/2 inch
              thick to both sides of the wall (if possible) to a
              height of 2 inches above the salt
              crystallization/evaporation zone.

         4.   As the render surface begins to stiffen, roughen it
              with the fine-toothed edge of a hacksaw blade.  The
              salts from the wall will migrate into the render.
              As the salts crystalize, the render will begin to
              crack and crumble.

         5.   Completely remove the dried render from the surface
              using a stiff bristle (non-metallic) brush.

         6.   Thoroughly rinse the surface with clean, clear
              water and allow to dry.

         7.   Repeat the entire application process as necessary
              to achieve the desired level of cleanliness.

3.02 ADJUSTING/CLEANING

    A.   Upon completion of the masonry cleaning work, clean
         window glass and spattered adjacent surfaces.

                         END OF SECTION