REMOVING DIRT BUILD-UP FROM SLATE SHINGLES


PART 1---GENERAL

1.01 SUMMARY

     A.   This procedure includes guidance on removing surface dirt
          from slate shingles.

     B.   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 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.   For Light Dirt:

          1.   Murphy's oil soap

     B.   For Heavy Dirt Build-up and Staining:

          1.   Oxalic Acid (COOH)2 or (H2C2O4):

               a.   A poisonous strong acid that occurs in various
                    plants as oxalates and is used especially as a
                    bleaching or cleaning agent and in making
                    dyes.

               b.   Other chemical or common names include
                    Ethanedioic acid.

               c.   Potential Hazards:  TOXIC; CORROSIVE TO
                    CONCRETE, STEEL, WOOD OR GLASS.

               d.   Available from chemical supply house, dry
                    cleaning supply distributor, drugstore or
                    pharmaceutical supply distributor, hardware
                    store, or photographic supply distributor (not
                    camera shop).  (Often sold under a
                    manufacturer's brand name; the chemical name
                    may appear on the label.)

          -OR-

               Muriatic Acid (generally available in 18 degree and
               20 degree Baume solutions):

               a.   A strong corrosive irritating acid.

               b.   Other chemical or common names include
                    Chlorhydric acid; Hydrochloric acid (30-35%);
                    Hydrogen chloride; Marine acid*; Spirit of
                    salt*; Spirit of sea salt*.

               c.   Potential Hazards:  TOXIC, CORROSIVE TO FLESH;
                    CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS,
                    FLAMMABLE.

               d.   Available from chemical supply house,
                    drugstore or pharmaceutical supply
                    distributor, or hardware store.

     C.   Clean, potable water

2.02 EQUIPMENT

     A.   Clean, soft cloths

     B.   Stiff bristle brush


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

     A.   For Light Dirt:

          1.   Apply Murphy's oil soap to the slate and rub with a
               clean, soft cloth.

          2.   Thoroughly rinse the slate with clean, clear water
               and allow to dry.

     B.   For Heavy Dirt Build-up and Staining:

          1.   Mix oxalic acid with water using proportions
               recommended by manufacturer.

               -OR-

               Mix 1 part muriatic acid with 3 parts water.

               CAUTION:  ALWAYS WEAR RUBBER GLOVES AND SAFETY
               GLASSES WHEN WORKING WITH ACID; ALWAYS POUR ACID
               INTO WATER (NEVER THE REVERSE); KEEP A PAIL OF
               WATER HANDY TO QUICKLY NEUTRALIZE ANY DAMAGE CAUSED
               BY SPILLAGE.

          2.   Apply the cleaning solution to the slate and rub
               with a clean, soft cloth.  Use a stiff bristle
               brush to aid in dirt removal.

          3.   Thoroughly rinse the slate with clean, clear water
               and allow to dry.

          4.   Repeat as necessary to achieve the desired level of
               cleanliness.

                          END OF SECTION