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Historic Preservation - Technical Procedures

Spectitle:

Removing Dirt From Stone Masonry Using The Water-Soak Method

Procedure code:

0440003P

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Stonework

Last Modified:

02/24/2012

Details:

Removing Dirt From Stone Masonry Using The Water-Soak Method



REMOVING DIRT FROM STONE MASONRY USING THE WATER-SOAK METHOD


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing dirt build-up
         on masonry using the water-soak method.  Prolonged
         saturation with water will cause the dirt to expand and
         contract at a much faster rate than the stone, causing it
         to crack away from the surface.

    B.   Water washing of stone masonry may be used periodically
         to remove dust, dirt, accumulations of grime or airborne
         pollutants which settle on the stone and do not get
         washed off by the natural action of wind-driven
         rainwater.

    C.   Advantages of the Water-Soak Method:  

         1.   Effective for cleaning heavily deteriorated ornate
              masonry that can not withstand pressure washing or
              abrasive cleaning techniques.

         2.   It allows use of mild cleaning agents and
              techniques for effective removal of severe carbon
              encrustations.

    D.   Limitations of the Water-Soak Method:  

         1.   EFFECTIVE ONLY ON CALCAREOUS STONE SUCH AS
              LIMESTONE--NOT RECOMMENDED FOR CLEANING BRICK,
              TERRA COTTA, GRANITE, SANDSTONE, BROWNSTONE AND
              MANY OTHER NON CALCAREOUS SURFACES.

         2.   This is an expensive, time-consuming process.  It
              is not the most practical method for cleaning an
              entire building facade.  It is most appropriate for
              use on small surface areas.

         3.   Thorough testing is required.  Prolonged exposure
              to water may result in oxidation of natural
              components of the masonry and may transport
              deleterious salts deep into the masonry.

         4.   Thoroughly saturated masonries may take several
              months to dry.

         5.   Water soaking procedures must be scheduled when
              there is no threat of freezing temperatures
              throughout the cleaning and drying process.

         6.   Cascading water used in this process may result in
              erosion of the wash surfaces.

         7.   Scaffolding and rigging requirements for this
              procedure are more elaborate.

         8.   Prolonged exposure to water may result in damage to
              interior surfaces, furnishings and equipment.

    E.   Safety Precautions:  

         1.   Precautions should be taken to guard against
              unnecessary water infiltration.  Monitors should be
              set within the walls to determine moisture content
              and possible problems.

         2.   Caution should be provided concerning possible
              oxide `blooms' caused by some masonry cleaners,
              including the water soak process.

    F.   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).

    G.   See also 04400-02-P and 04400-02-P for alternative
         guidance on removing dirt from stone masonry.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Clean, potable water (preferably mineral water)

2.02 EQUIPMENT

    A.   Garden hose and nozzle (size appropriate for very fine
         misting)

    B.   Fan-shaped spray-tip which disperses water at angle of
         not less than 15 degrees.

    C.   Non-metallic brushes (no iron or brass wire)

    D.   Wood scrapers


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Observe all precautions to protect the building
              from excess water infiltration and to protect
              adjacent property and persons from water over-spray
              and run-off damage.

         2.   Before proceeding with work, check to see that
              there are no open joints or cracks and that
              windows, doors and other points of entry are
              securely covered to prevent entry of water into the
              building.

3.02 ERECTION/INSTALLATION/APPLICATION

    A.   Water-soak a test area of approximately 100 SF:

         1.   Hang or support a 1/2-inch plastic pipe water spray
              array under a designated section to thoroughly and
              uniformly wet the area, soften any gypsum
              encrustation, and prepare it for final rinsing off
              with a plain water pressure washing.

         2.   Connect the spray array to a building water hydrant
              with 5/8-inch garden hose as required.

         3.   Fit the plastic pipe array with four to six fixed
              fine spray or mist garden sprinkler heads to cover
              the area and wet all face and side surfaces.

         4.   Provide a mechanical or electric timer control
              valve with adjustable time settings, lawn sprinkler
              type, with the capability of cycling the spray
              water on and off continuously for four hour cycles,
              or other timed periods as directed, 24-hours per
              day.

    B.   Following approval of the test installation, operate the
         water soak test spray system for a 24 hour period with a
         repeat test as directed.

    C.   Follow the 24 hour water soaking by a plain water
         pressure washing (see 04400-01-P for guidance).

         1.   The Contracting Officer should record the
              effectiveness of the cleaning.

         2.   As Contracting Officer directs, include a repeat
              test cleaning on the same area, with a different
              timed cycle for sprays, for up to an additional 48
              hour period followed by the same pressure wash
              rinse and Contracting Officer's observation.

         3.   The repeat test may be waived by the Contracting
              Officer if the initial test results are conclusive.

    D.   Following approval of the test cleaning, spray the
         masonry with a fine mist of water over a prolonged period
         of time under the conditions approved by the Contracting
         Officer and the RHPO.  

         1.   The spray should never be pointed directly at the
              surface.  The spray should be fine and use
              approximately 110 to 140 liters of water per hour
              (45 liters per hour for delicate detailing).

         2.   Prolonged saturation with water will eventually
              loosen any heavy dirt or crusts (it may take from
              4-6 hours to a week or more).

         3.   When the dirt has softened, remove it by hand-scrubbing
              with non-metallic brushes or by using a moderate-pressure
              water wash (see 04400-01-P); Use a wooden scraper to
              remove heavy sulphate crusts.

                         END OF SECTION