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Historic Preservation - Technical Procedures

Spectitle:

Removal Of Soiling From Sandstone Prior To Repointing

Procedure code:

0447005R

Source:

Internet - University Of Vermont

Division:

Masonry

Section:

Sandstone

Last Modified:

11/13/2012

Details:

Removal Of Soiling From Sandstone Prior To Repointing



REMOVAL OF SOILING FROM SANDSTONE PRIOR TO REPOINTING


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 THE
POROUS STONE.  USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY
FOR THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.

SOME DEGREE OF AGING, WEATHERING AND COSMETIC DEFECT IS NATURAL
AND ACCEPTABLE AND CONTRIBUTES TO THE BUILDING'S CHARACTER.
NATURAL WEAR AND WEATHERING SUCH AS DEPRESSIONS IN THE STONE MAY
NOT BE SUFFICIENT CAUSE FOR REPAIR.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing biological
         growth, surface dirt and efflorescence from sandstone
         surfaces prior to repointing.

         CAUTION: DO NOT CLEAN SANDSTONE FREQUENTLY.  THIS MAY
         CAUSE A PREMATURE BREAKDOWN OF THE BONDING AGENTS OR
         CEMENTIOUS MATERIAL THAT BINDS THE STONE TOGETHER.

    B.   Sandstone is very porous and prone to picking up dirt,
         dust, oils, and greases from both direct contact and from
         the atmosphere. The absorption of these kinds of
         contaminants can cause surface staining, and promote
         biological growth.

    C.   Biological growths such as lichens, algae, moss and fungi
         growing on stone walls is usually an indication that
         there is excess moisture in or around the stone.  These
         growths should be removed, as they attract moisture to
         the stone surface and hold it there, which can lead to
         more serious problems.  Lichens and mosses in particular,
         produce oxalic acid which can damage certain types of
         historic stone.


    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).


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.  Rohm & Haas (subsidiary of Dow Chemical)
         www.rohmhass.com
         

    B.  Sigma-Aldrich Corporation
         www.sigma-aldrich.com
         

2.02 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.   Non-ionic Detergents such as "Triton" (Rohm & Haas),
         "Igepal" (Sigma-Aldrich), or approved equal.

    B.   Bleach:  

         CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, AS CHLORINE GAS,
         (POISONOUS GAS) WILL RESULT!  DO NOT USE BLEACH ON BIRD
         DROPPINGS.

         1.   Other chemical or common names include Bleaching
              solution*; Household bleach*; Laundry bleach*; Sodium
              Hypochlorite (NaOCl); Solution of chlorinated soda*.

         2.   Potential Hazards:  CORROSIVE TO FLESH.

         3.   Available from chemical supply house, grocery store
              or supermarket, hardware store or janitorial supply
              distributor.

    C.   Clean, potable water

2.03 EQUIPMENT

    A.   Stiff natural bristle brush

    B.   Low pressure sprayer or garden hose

    C.   Polyethylene sheet

    D.   Wooden spatula or tongue depressors


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Determine the source of excessive moisture, i.e. leaky
         downspout, standing water, roof overhang, vegetation,
         etc., and make any necessary repairs before continuing
         with this task.

    B.   Determine the type of stain, i.e. algae and lichens, mold
         and mildew, or efflorescence.

3.02 PREPARATION

    A.   Protection:  

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

         2.   Do not spray in the immediate vicinity of
              unprotected people, landscaping, and animals.

    B.   Surface Preparation: Temporarily fill large cracks with
         foam backer rod before areas are cleaned to avoid the
         infiltration of large amounts of water.

3.03 ERECTION, INSTALLATION, APPLICATION

    CAUTION: DO NOT USE ABRASIVE CLEANING METHODS.  DO NOT USE
    ACIDIC OR ALKALI CHEMICAL CLEANERS.  ALWAYS USE THE GENTLEST
    MEANS OF CLEANING POSSIBLE.

    A.   For Crumbly Caulking Compound:

         1.   Remove the flaking caulking compound using wooden scrapers
              or tongue depressors.  Take care not to gouge or
              damage the stone.

         2.   Remove as much as possible using a stiff bristle
              brush.

              CAUTION: DO NOT USE STEEL WIRE BRUSHES AS THEY MAY
              LEAVE BEHIND BITS OF IRON, WHICH COULD RUST AND
              LEAVE STAINS ON THE SURFACE.  DO NOT USE POWERED
              ROTARY BRUSHES.  THESE ARE TOO HARSH AND MAY
              SEVERELY ABRADE THE SURFACE.

         3.   Small amounts of residual caulking compound may
              remain on the surface, and should be left alone.
              DO NOT USE SOLVENTS TO REMOVE THIS RESIDUE.  It is
              likely that this residue will weather away
              naturally and cause no physical harm to the stone.

         4.   Retain silicone caulking compounds which may have
              been applied to help seal some flashing joints, and
              make repairs if necessary.

    B.   For Loose Dirt and Dust, Bird Droppings:

         1.   Wash the surface with water using a low-pressure
              sprayer or garden hose with a fine spray.

         2.   Gently scrub as necessary with a wet natural
              bristle or plastic bristle brush.

         3.   If necessary, add a non-ionic detergent to the
              sprayer at the lowest effective concentration.
              Note:  Test a small area to see that it does not
              leave behind a hazy residue.

         4.   Avoid soaking the stone. Rinse the surface
              thoroughly to prevent hazy or invisible residues
              which may attract dirt.

    C.   For Molds, Mosses, and Algae: Fungal/algal growth is
         fostered in environments high in moisture.  This,
         combined with lack of sunlight, creates favorable
         conditions for this type of surface staining.

         1.   Eliminate conditions of excess moisture.

         2.   Carefully scrub the surface with a natural bristle
              or plastic brush and water.

         3.   If necessary, add a small amount of bleach to the
              water to help kill the plant growth.  

    D.   For Efflorescence and Surface Salts:

         1.   Carefully dry-brush salts off the surface using a
              natural bristle brush or wash with water.

         2.   If the efflorescence returns, carefully examine
              surrounding areas to determine the possibility of
              leaks or sources of water causing excess moisture
              infiltration.

         3.   Eliminate sources of excess moisture and repeat
              D.1. above.

    E.   For guidance on repointing, see 04470-06-R.

                         END OF SECTION
 


removing soiling sandstone, sandstone soiling, cleaing sandstone