Removing Dirt From Limestone Ornament Using A Hot Lime Poultice
- Procedure code:
- Developed For Hspg (Nps - Sero)
- Last Modified:
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 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.
- Baker's Lime Method is a 4-stage process which includes cleaning, repair, consolidating and preserving.
- 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:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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.
A. Lime putty
B. Burlap or cheesecloth
C. Plastic sheeting
E. Clean potable water
A. Hand spray bottle
B. Dental picks
C. Small, soft bristle brushes
D. Trowels and spatulas
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).