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Historic Preservation - Technical Procedures

Spectitle:

Removing Dirt From Limestone Ornament Using A Hot Lime Poultice

Procedure code:

0446001R

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Limestone

Last Modified:

02/24/2012

Details:

Removing Dirt From Limestone Ornament Using A Hot Lime Poultice



REMOVING DIRT FROM LIMESTONE ORNAMENT USING A HOT LIME POULTICE


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 cleaning dirt from
         limestone using a hot lime poultice - also known as
         Baker's Lime Method.  Developed by Robert Baker in the
         1950's, THIS METHOD OF DIRT REMOVAL IS LABOR INTENSIVE
         AND, THEREFORE, IS BEST USED ON HIGHLY SIGNIFICANT
         ARCHITECTURAL DETAILS.

         1.   Baker's Lime Method is a 4-stage process which
              includes cleaning, repair, consolidating and
              preserving.

         2.   This procedure describes the cleaning stage.  Other
              stages in the process are described in 04460-02-R.

    B.   Dirt may consist of particles of dust, sand or grit, or
         tarry soot.  Particulate dirt or soiling may result from
         vehicular or human traffic or from pollutant or sulfate
         crusts building up in protected areas not regularly
         washed by rain.  Pollutant crusts hasten masonry
         dissolution and should be removed.

    C.   Safety Precautions: Check manufacturer's literature for
         precautions and effects of products and procedures on
         adjacent building materials, components, and especially
         vegetation. Take appropriate protective measures.

    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 limestone, see 04460-01-S.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Lime putty

    B.   Burlap or cheesecloth

    C.   Plastic sheeting

    D.   String

    E.   Clean potable water

2.02 EQUIPMENT

    A.   Hand spray bottle

    B.   Dental picks

    C.   Small, soft bristle brushes

    D.   Trowels and spatulas


PART 3---EXECUTION

3.01 ERECTION/INSTALLATION/APPLICATION

    A.   Thoroughly wet the stone with clean water.

    B.   Using a trowel, press lime putty into the affected
         limestone ornament.

    C.   After a thick coat has been applied, bind it with wet
         burlap or cheesecloth; Secure it with string.

    D.   Loosely tie a heavy-duty polyethylene sheet around the
         ornament.

    E.   Keep the ornament covered for about 2-3 weeks.

    F.   Periodically, lift the sacking during that time and spray
         the poultice with water to keep the poultice damp.

    G.   Carefully lift off the lime in small portions using
         spatulas or small trowels (use water sprays to help
         loosen the poultice).

    H.   Much of the dirt will not immediately detach with the
         poultice material; The poultice moistens the dirt so that
         it can be removed more easily by washing and brushing.

    I.   Using hand sprays, dental picks, small tooth brushes or
         stencil brushes, gently remove loosened dirt left on the
         stone surface.

    J.   If, after cleaning, there is any evidence of stone
         damage, attempt limestone surface repair using
         consolidation and lime mortar (see 04460-02-R).

                         END OF SECTION