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 poisonous strong acid that occurs in various plants as oxalates and is used especially as a bleaching or cleaning agent and in making dyes.
   • Other chemical or common names include Ethanedioic acid.
   • Potential Hazards: TOXIC; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.
   • 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.)
2. -OR-
3. 
   Muriatic Acid (generally available in 18 degree and 20 degree Baume solutions):
   • a. A strong corrosive irritating acid.
   • Other chemical or common names include Chlorhydric acid; Hydrochloric acid (30-35%); Hydrogen chloride; Marine acid*; Spirit of salt*; Spirit of sea salt*.
   • Potential Hazards: TOXIC, CORROSIVE TO FLESH; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS, FLAMMABLE.
   • 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.