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Historic Preservation - Technical Procedures

Spectitle:

Removing Painted Graffiti From Sandstone

Procedure code:

0447009R

Source:

National Capitol Region Specifications - Itc Building

Division:

Masonry

Section:

Sandstone

Last Modified:

12/16/2014

Details:

Removing Painted Graffiti From Sandstone



REMOVING PAINTED GRAFFITI FROM SANDSTONE


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

    A.   This procedure includes guidance on the removal of
         paint-based graffiti from sandstone using a chemical
         paint stripper or poultice.  For additional information
         and/or alternative methods of removing graffiti from
         sandstone, see 04200-01-S.

    B.   Latex paints tend to remain primarily on the surface of
         stone materials as opposed to oil based paints, which
         tend to penetrate into the stone and remain there.

    C.   Historic Structures Precautions:

         1.   Do not use acids or flame tools to strip paint
              from stone, as it will damage the surface.

         2.   Do not use steel or metal spatulas or tools to
              scrape stone because of the likelihood of
              scratching, chipping, gouging, or otherwise
              marring the surface.

    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 sandstone, see 04470-01-S.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.  ProSoCo, Inc.
         www.prosoco.com


2.02 MATERIALS

    A.   Paint Stripper to remove multiple layers of paint
         coatings and graffiti from exterior masonry surfaces
         (remains active for up to 24 hours), such as "Sure
         Klean Heavy Duty Paint Stripper" (ProSoCo, Inc.), or
         approved equal.

         NOTE:  AVOID COMMERCIAL STRIPPERS WHICH CONTAIN WAX,
         CHOOSING INSTEAD THE "WASHABLE IN WATER" TYPES.

    B.   Clean, potable water

    C.   Clean, natural fiber rags for drying

    D.   Solvents such as acetone or denatured alcohol:

         Acetone (C3H6O):

         1.   A volatile fragrant flammable liquid ketone used
              chiefly as a solvent and in organic synthesis and
              found abnormally in urine.

         2.   Other chemical or common names include Dimethyl
              ketone; Propanone

         3.   Potential Hazards:  VOLATILE AND FLAMMABLE SOLVENT

         4.   Available from chemical supply house or hardware
              store.

         Denatured Alcohol:

         1.   Other chemical or common names include Methylated
              spirit*.

         2.   Potential hazards:  TOXIC AND FLAMMABLE.

         3.   Available from hardware store, paint store or
              printer's supply distributor.

         4.   Denatured alcohol should be a satisfactory
              substitute for ethyl alcohol for stain removing
              purposes.

    E.   Filler material such as attapulgite clay, kaolin,
         fuller's earth, talc, chalk, cotton pads, acid-free
         paper.  (Do not use chalk or iron-containing clay with
         an acid solvent as their chemical reaction will cancel
         the effectiveness of the acid).

2.03 EQUIPMENT

    A.   Garden hose and nozzle

    B.   Wood or plastic spatulas


    C.   Stiff fiber or jute bristle brushes (No Metallic)


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Examine the sandstone surface CAREFULLY to determine
         the cause of staining before proceeding with any
         cleaning operation.

    B.   Identify the substance used to create the graffiti.

    C.   Examine the surrounding area for signs of what may have
         been used to create the graffiti (i.e. spray cans or
         other debris).

3.02 ERECTION, INSTALLATION, APPLICATION

    NOTE:  SANDBLASTING OR OTHER ABRASIVE TECHNIQUES TO REMOVE
    PAINT SHOULD BE AVOIDED. INSTEAD SMALL TEST PATCHES SHOULD
    BE TRIED USING SUCH SOLVENTS AS ACETONE, DENATURED ALCOHOL,
    AND COMMERCIAL PAINT STRIPPERS.

    A.   Thoroughly rinse the stained area with clean, clear
         water, while carefully removing loose paint using a
         wooden scraper.  Allow surface to thoroughly dry.

    B.   Brush apply a coat of commercial paint stripper over
         the surface (approximately 1/8" thick), and allow to
         dwell until paint is lifted from the surface; follow
         manufacturer's instructions.

         -OR-

         Brush apply a solvent such as acetone or detatured
         alcohol.

    C.   Scrape off softened paint with a wooden spatula.

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

    E.   Repeat the process as necessary to sufficiently remove
         the stain.

    F.   For stubborn paint stains, poulticing may be required.

         1.   Create a poultice by mixing an appropriate solvent
              with a filler material.

         2.   Apply the mixture to the stained area in a 1/4" to
              3/4 " thick layer using a wood or plastic spatula
              and allow to dry.  Be sure to spread the poultice
              well beyond the stained area.  The liquid portion
              of the paste will migrate into the masonry where
              it will dissolve some of the staining material.
              Then the liquid will gradually move back beyond
              the masonry surface and into the poultice, where
              it will evaporate, leaving the dissolved staining
              material in the poultice.

         3.   Allow poultice to dwell, keeping it moist until
              the stain has lifted.  Secure a polyethylene sheet
              over the poultice to reduce evaporation.  Exact
              length of dwell time will vary and will require
              periodic inspection of the substrate.

         4.   Once it appears that the stain has lifted, allow
              the poultice to dry out.  As the poultice dries,
              the solvent is re-absorbed by the poultice
              material bringing with it the stain.

         5.   The poultice should fall off naturally as it
              dries.  Remove remaining material with a wooden
              spatula and natural bristle brush.

         6.   Rinse the surface thoroughly with clean, clear
              water and allow to dry.  

         7.   Repeated applications of poultice may be required.

3.03 ADJUSTING/CLEANING

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

                         END OF SECTION
 


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