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Historic Preservation - Technical Procedures

Spectitle:

Removing Dirt From Stone Masonry By Pressure Washing

Procedure code:

0440001P

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Stonework

Last Modified:

06/13/2012

Details:

Removing Dirt From Stone Masonry By Pressure Washing



REMOVING DIRT FROM STONE MASONRY BY PRESSURE WASHING


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing dirt build-up
          on masonry by pressure washing with water and mild
         detergents.  This technique is effective for removal of
         light to moderate atmospheric and organic staining.  It
         may also be used to remove any residual traces of
         chemicals used in other cleaning treatments.

    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 Pressure Washing:  

         1.   Surface staining and loose surface debris may be
              removed more quickly.

         2.   May be used effectively in conjunction with
              chemical cleaning agents or abrasive materials;
              however, see limitation under 1.01 D.8.

         3.   The amount of time spent scraping and scrubbing may
              be substantially reduced when appropriate rinsing
              pressures and water volumes are used.

    D.   Limitations of Pressure Washing:

         1.   When used independently, this technique is
              generally not effective in removing severe
              staining.

         2.   Excessively high water pressures and flow rates may
              have an abrasive effect and may accelerate masonry
              decay.

         3.   Extreme exposure to water can result in oxidation
              of natural components of the masonry.

         4.   Water-saturated masonry may take several weeks to
              dry thoroughly.

         5.   Cleaning procedures must be scheduled when there is
              no threat of freezing temperatures.

         6.   Prolonged exposure to water or water entering
              through voids in the wall system may result in
              damage to interior surfaces, furnishings, and
              equipment.

         7.   Excessive pressure can erode mortar joints and
              force water to the interior.

         8.   Water, even at low pressure, in combination with a
              grit or abrasive material can cause damage to
              historic materials.

         9.   Water runoff must be controlled to prevent
              intrusion into basement areas and surrounding
              properties.

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

    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 04400-03-P for alternative
         guidance on removing dirt from stone masonry.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.  Dow Chemical
         www.dow.com   
         
    B.  Union Carbide Corporation
         www.unioncarbide.com                  

    C.   Ashland Chemical
         www.ashland.com
        
        

2.02 MATERIALS

    A.   Non-ionic detergent such as "Tergitol",

          "Triton", "Igepal", or approved equal.

         1.   Use dilution as approved by testing on material to
              be cleaned.

         2.   Acidic or alkaline products are NOT acceptable.

    B.   Clean, potable water (preferably mineral water)

2.02 EQUIPMENT

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

    B.   Spray Equipment:  Provide equipment for controller spray
         application of water and cleaners, if any, at rates
         specified by RHPO for pressure, measured at spray tip,
         and for volume.

         1.   For spray application of cleaners provide low-pressure
               tank or pump suitable for cleaner selected, equipped with
               cone-shaped spray-tip.

         2.   For spray application of water provide fan-shaped
              spray-tip which disperses water at angle of not
              less than 15 degrees.

    C.   Assorted Washing Brushes (available from local janitorial
         supply houses or hardware stores):

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

         2.   Tampico fiber set in a hardwood block

         3.   A "whitewash brush" (ideal for most purposes)

         4.   "Parts washing" brushes (useful for small areas and
              crevices)

    D.   Wood scrapers

    E.   Buckets, molded rubber or plastic, such as the "Fortex"
         molded rubber pail - 12 or 14 quart size

    F.   Rubber gloves and rain gear, if desired

    G.   Toweling or rags, clean, lint-free


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Cleaning methods should be tested prior to
              selecting the one for use on the building; The
              simplest and least aggressive methods should be
              selected.

         2.   The level of cleanliness desired should be
              determined; A new appearance look is both
              inappropriate and requires an overly harsh cleaning
              method.

         3.   Prolonged exposure of water causes rapid
              deterioration in older structures.

         4.   Take precautions to ensure that the water does not
              penetrate the surface and cause damage to the
              interior of the structure.

         5.   This procedure may cause corrosion of hidden iron
              work and steel anchors causing either staining or
              cracking due to the rapid expansion of the metal.

         6.   If the masonry remains saturated during the first
              frost, surface pieces may spall off as the water
              freezes.

         7.   Iron and chloride in the water can cause
              disfigurement and staining.

    B.   Surface Preparation:

         1.   Fill the buckets, usually one or two, with about
              two gallons of water.

         2.   Beginning at the top and gradually working down,
              scrub lightly with the fiber brush to remove any
              superficial deposits.  Take care to avoid
              scratching or otherwise damaging any polished
              surfaces.

         3.   Rinse with clean, clear water.

         4.   Dry with clean, lint-free toweling or rags.

         5.   Tenacious mineral deposits may be treated locally
              with gentle abrasion using wooden paddles or
              sticks.  Great care should be exercised to avoid
              damaging the highly polished surfaces of masonry
              where they exist.

3.02 ERECTION/INSTALLATION/APPLICATION

    NOTE:  THIS PROCEDURE SHOULD BE USED IN CONJUNCTION WITH
    04510-04-S FOR GUIDANCE ON USING HIGH PRESSURE CLEANING
    EQUIPMENT.

    NOTE:  LOW-PRESSURE WASH SHOULD MEASURE BETWEEN 100 PSI AND
    400 PSI.  MEDIUM-PRESSURE WASH SHOULD MEASURE BETWEEN 400 PSI
    AND 800 PSI.  HIGH-PRESSURE WASH MEASURES BETWEEN 800 PSI AND
    1200 PSI.

    A.   General:  

         1.   Spray-apply water to masonry surfaces to comply
              with requirements specified by RHPO for location,
              purpose, water temperature, pressure, volume and
              equipment.

         2.   Heat water, if required, to effectively aid dirt
              removal and to clean surfaces.

         3.   Clean with spray nozzle tip held consistently a
              minimum of 12-inch distance from masonry surface
              and direction of stream perpendicular to the
              surface unless other working distances and angles
              of spray direction are approved by cleaning tests.

         4.   Keep spray stream moving across the masonry surface
              at a uniform rate at all times.

              a.   Shut off flow before stopping motion at the
                   end of a sweep, and begin the sweep motion
                   before opening flow.

              b.   Normal sweep motion is horizontal, side to
                   side; however, a vertical pattern may be used
                   where necessary.

              CAUTION:  "BORING IN" WITH SPRAY SHOULD BE AVOIDED.
              CONCENTRATING SPRAY STREAM AT A POINT; USING TOO
              HIGH OF A PRESSURE; AND WORKING AT A LESS THAN
              APPROVED DISTANCE, CAN SERIOUSLY DAMAGE THE MASONRY
              AND MAY BE CAUSE FOR REJECTING THE WORK AND REASON
              TO REQUIRE ADDITIONAL REPAIRS.

    B.   Low-Pressure and Medium-Pressure Water Washing:

         1.   Hand-brush and scrape heavy grime prior to washing
              (see Section 3.01 B. above).

         2.   Take a common garden hose and power-wash the face
              of the building, gradually increasing the water
              pressure as needed to sufficiently loosen the dirt.

         3.   Allow to dry, and if additional cleaning is
              required, try the following:

    C.   Low-Pressure and Medium-Pressure Water Washing
         Supplemented with Non-Ionic Detergents:

         1.   Hand-brush and scrape heavy grime prior to washing
              (see Section 3.01 B. above).

         2.   Wash the masonry using a low-to-medium-pressure
              wash, adding a non-ionic detergent (see Section
              2.02 A. above).

         3.   Hand-brush as needed with non-metallic brushes.

         4.   Rinse cleaned work with pressure wash spray as for
              cleaning to thoroughly remove loosened dirt, dirty
              cleaning water, and cleaner residue from surfaces.

              a.   Test rinse water residue on the masonry
                   surface with pH indicating test strips
                   regularly and record results in daily work log
                   for review by RHPO.

              b.   Re-rinse/clean with clear water any area where
                   the pH indicator strips show that there is
                   residual acidity or alkalinity on the surface
                   and allow to dry.

                         END OF SECTION
 


dirt on masonry, pressure wash, water spray