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Historic Preservation - Technical Procedures

Spectitle:

Removing Old Sulphated Limewash From Masonry

Procedure code:

0420006R

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Unit Masonry

Last Modified:

02/24/2012

Details:

Removing Old Sulphated Limewash From Masonry



REMOVING OLD SULPHATED LIMEWASH FROM 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 THE 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 old
         sulphated limewash from masonry by poulticing with
         hydrochloric acid.

    B.   IT IS VERY DIFFICULT TO REMOVE OLD SULPHATED LIMEWASH
         FROM MASONRY WITHOUT CAUSING DAMAGE TO THE SURFACE BELOW.
         THEREFORE, LIMEWASHES SHOULD ONLY BE REMOVED WHEN IT IS
         ABSOLUTELY DESIRABLE AND SHOULD ONLY BE PERFORMED BY A
         TRAINED PROFESSIONAL.

    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

    NOTE:  Chemical products are sometimes sold under a common
    name.  This usually means that the substance is not as pure as
    the same chemical sold under its chemical name.  The grade of
    purity of common name substances, however, is usually adequate
    for stain removal work, and these products should be purchased
    when available, as they tend to be less expensive.  Common
    names are indicated below by an asterisk (*).

    A.   Hydrochloric Acid (30-35%):

         1.   Other chemical or common names include Chlorhydric
              acid; Hydrogen chloride; Muriatic acid* (generally
              available in 18 degree and 20 degree Baume
              solutions); Marine acid*; Spirit of salt*; Spirit
              of sea salt*.

         2.   Potential hazards:  TOXIC; CORROSIVE TO FLESH;
              CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS;
              FLAMMABLE.

         3.   Available from chemical supply house, drugstore or
              pharmaceutical supply distributor, or hardware
              store.

    B.   Filler for poulticing such as attapulgite or sepiolite
         clay:  Available from hardware store.

    C.   Clean, potable water

    D.   Plastic sheets for covering poultice

2.02 EQUIPMENT

    A.   Wood or plastic spatula

    B.   Phosphor bronze or bristle brushes

    C.   Air abrasive tools (suction or pressure)


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Provide adequate wash solutions (i.e. water, soap
              and towels) before starting the job.

         2.   Whenever acid is used, the surface should be
              thoroughly rinsed with water as soon as its action
              has been adequate.  Otherwise it will continue
              etching the masonry even though the stain is gone.

3.02 ERECTION/INSTALLATION/APPLICATION

    NOTE:  UNDER NO CIRCUMSTANCES ARE THESE TECHNIQUES TO BE USED
    ON SCULPTURE OR IMPORTANT DETAILS.

    NOTE:  DO NOT TRY MORE THAN ONE TREATMENT ON A GIVEN AREA
    UNLESS THE CHEMICALS USED FROM PRIOR TREATMENT HAVE BEEN
    WASHED AWAY.

    A.   Soften the limewash by applying a poultice:

         1.   Mix attapulgite or sepiolite clay with water to
              form a thick paste.

         2.   Thoroughly wet the area to be treated with clean,
              clear water.

         3.   Apply the poultice over the limewash using a wood
              or plastic spatula and cover with plastic to keep
              it damp.

         4.   When the poultice has dried, brush or scrape it off
              with a wooden scraper.  

    B.   Break down the limewash surface by scrubbing with a
         phosphor bronze or bristle brush and hot water; Hot water
         should be used if the limewash has an oil or tallow
         binder.

    D.   If residual traces remain, wet the wall again with hand
         sprays and wash with a 30-35% solution of hydrochloric
         acid.

    E.   Thoroughly rinse the surface with clean water and allow
         to dry.

    F.   Repeat as necessary to achieve the desired level of
         cleanliness.

                         END OF SECTION