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
          Independence Mall West
          Philadelphia, PA  19105
          215/592-3000

     B.   GAF Corporation
          1361 Alps Road
          Wayne, NJ  07470

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" (GAF Corporation), or approved equal.

     B.   Bleach:  

          CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, A
          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 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 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