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Removing Dirt Build-Up On Sandstone
REMOVING DIRT BUILD-UP ON SANDSTONE
PART 1---GENERAL
1.01 SUMMARY
A. This procedure includes guidance on cleaning selected
areas of dirt-build-up on sandstone by washing with an
alkaline cleaner (for calcareous sandstone), or by
washing with a hydrofluoric acid-based cleaner (for most
other sandstones). GENERALLY, THIS WORK SHOULD BE
PERFORMED BY AN EXPERIENCED CONTRACTOR.
B. For precautions relating to pressure washing, see 04510-
04-S.
C. 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).
1.02 QUALITY ASSURANCE
A. Qualifications: Minimum 10 years experience in historic
masonry cleaning.
B. Reference Standards:
1. Secretary of the Interior's "Standards for
Rehabilitation" (see 01091-04-S).
2. Preservation Brief No. 1, "The Cleaning and
Waterproofing of Historic Masonry Buildings" (see
04510-06-S).
C. Test Panels: Each alternative method for each type of
cleaning.
PART 2---PRODUCTS
2.01 MANUFACTURERS
A. ProSoCo, Inc.
www.prosoco.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. For Calcareous Sandstone: Alkaline cleaners and water
rinse, such as "Sure-Klean 766 Limestone & Masonry Pre-Wash/After-wash"
(ProSoCo, Inc.), or approved equal. Suitable alkaline
cleaners will contain potassium hydroxide or aluminum
hydroxide.
B. For Most Sandstones, Excluding Calcareous: Hydrofluoric
acid-based cleaner containing not more than 5%
hydrofluoric acid such as "Sure-Klean Restoration
Cleaner" (ProSoCo, Inc.), or approved equal.
C. Acetic Acid:
1. A colorless pungent liquid acid that is the chief
acid of vinegar and that is used especially in
synthesis (as of plastics).
2. Other chemical or common names include Acetates*;
Acetous salts*; Salts or esters of acetic acid*Vinegar acid*.
(Vinegar itself, which contains about 4% acetic acid, may
be suitable for some purposes requiring acetic acid.)
3. Potential hazards: CORROSIVE TO FLESH AND
CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.
4. Available from chemical supply house (both
commercial and scientific), drugstore or
pharmaceutical supply distributor, grocery store or
supermarket, or hardware store.
D. Plastic sheeting
E. Clean, potable water
2.02 EQUIPMENT
A. Pressure water rinsing equipment (measuring between 100
and 400 psi for low-pressure; between 400 and 800 psi for
medium pressure).
B. Fan-type spray tips (15 degree fan spray)
C. Stiff fiber-bristle brushes
D. Plastic spatula
E. Masking tape
PART 3---EXECUTION
3.01 EXAMINATION
A. Examine site conditions to determine that current
drainage is sufficient for adequately and safely removing
cleaning waste and run-off from the site.
B. Test clean a small, inconspicuous area to check for
adverse effects and damage to the material.
3.02 PREPARATION
A. Protection:
1. Protect surrounding materials on the site and
adjacent building surfaces and building landscaping from coming in contact
with the cleaning materials and run-off. Cover
with acid-resistant coatings when using acid-based
cleaners. Hydrofluoric acid can SEVERELY etch
aluminum and glass.
2. Provide workers with necessary protection against
cleaning chemicals, overspray and run-off.
3. Prevent cleaning chemicals from coming in contact
with any painted, polished or metallic surfaces.
4. Divert flow of run-off to drains in compliance with
municipal codes. Comply with municipal codes
regarding containment and disposal of cleaning
materials.
B. Surface Preparation:
1. Before proceeding with cleaning operations, remove
all miscellaneous hardware, anchors and bird
excrement from the surface to prevent any
discoloration.
NOTE: BIRD EXCREMENT IN CONTACT WITH CLEANING
SOLUTION WILL LEAVE A PERMANENT DARK-COLORED STAIN
ON THE SURFACE.
2. Check for open holes and joints in surface and
repaint or caulk as required to prevent water and
cleaning solutions from penetrating deeply into the
wall.
3.03 ERECTION, INSTALLATION, APPLICATION
NOTE: WHEN CLEANING, AVOID OVERCLEANING. AIM FOR ACHIEVING
85% CLEAN. MOST DAMAGE OCCURS WHEN ATTEMPTING TO CLEAN THE
LAST 15%.
NOTE: TEST CLEAN A SMALL AREA TO DETERMINE EFFECTIVENESS OF
CLEANING METHODS, MATERIALS, EQUIPMENT AND WORKING PRESSURES
SELECTED BEFORE PROCEEDING WITH CLEANING OPERATIONS ON LARGER
AREAS. ADJUST METHODS, MATERIALS, EQUIPMENT, PRESSURES, ETC. AS
NECESSARY. ALLOW TIME FOR TEST AREA TO COMPLETELY DRY TO ASSESS
CLEANING RESULTS AND TO DETERMINE IFTHERE ARE ANY MATERIAL
CHANGES THAT REQUIRE A MODIFICATION OF THE TREATMENT. DO NOT PROCEED
UNTIL AN ACCEPTABLE CLEANING OPERATION HAS BEEN APPROVED AND FULLY DOCUMENTED.
A. Pre-wet stone surface using a low pressure wash (between
100 and 400 psi).
B. Loosen dirt by scrubbing the area using a non-metallic
brush.
C. Flood the surface with medium-high water pressure (400-
600 psi)at a rate of three to four gallons per minute.
Rinse from top to bottom. KEEP THE STONE SURFACE MOIST
DURING THE ENTIRE CLEANING PROCESS IN ORDER TO AVOID THE
FORMATION OF RESIDUAL SALTS ON THE SURFACE.
D. FOR CALCAREOUS SANDSTONE, apply a commercial alkaline
cleaner. Follow manufacturer's application instructions.
CAUTION: DO NOT USE ACID-BASED CLEANERS ON CALCAREOUS
SANDSTONE. ACIDIC PRODUCTS CAN ETCH OR ABRADE THE STONE.
ALKALINE CLEANERS SHOULD ALWAYS BE USED ON ACID-SENSITIVE
MASONRY. AVOID USING ALKALINE SOLUTIONS CONTAINING
SODIUM HYDROXIDE (CAUSTIC SODA OR LYE) OR AMMONIUM
BIFLUORIDE. THESE HAVE THE POTENTIAL TO CAUSE
EFFLORESCENCE, SUBFLORESCENCE AND CAN LEAD TO ABRASION OF
THE SURFACE.
1. Apply alkaline cleaner pre-wash using a soft nylon
bristle brush. Allow to remain on the surface for
30 minutes, or as long as determined by testing.
2. Rinse the surface thoroughly with clean, clear
water using pressure between 400 and 600 psi.
Direct the spray downward to avoid forcing water into joints and the stone surface.
Monitor interior spaces at cleaning locations and contain water from rinsing operation so as not to
flood building interior.
3. While surface is still wet from rinsing off pre-
wash, apply limestone afterwash with a soft, fiber
bristled brush.
a. Dilute limestone afterwash with as much water
as determined effective during testing.
b. If surface has begun to dry, re-wet before
applying afterwash.
c. Cover all corners, moldings, and interstices
of the limestone.
4. Allow to stand for 3-5 minutes or as long as
determined by testing.
5. Rinse the surface thoroughly with clean, clear
water using pressure between 400 and 600 psi. Direct spray downward as noted above.
Monitor interior spaces and contain water from rinsing operation so as not to
flood building interior.
6. Spray on an application of Acetic Acid in order to
neutralize the alkaline wash.
7. Rinse the stone with clean, clear water again.
8. For very light calcareous sandstone, the use of a
complexing agent such as EDTA or organic bleach may
be required in order to achieve uniform results.
USE ONLY UNDER PROFESSIONAL SUPERVISION.
E. For Most Sandstones, (EXCLUDING CALCAREOUS SANDSTONE),
apply a commercial hydrofluoric acid-based cleaner.
Follow manufacturer's application instructions.
CAUTION: HYDROFLUORIC ACID MAY LIGHTEN THE COLOR OF SOME
SANDSTONES CONTAINING IRON. DO A TEST PATCH IN NOT HIGHLY VISIBLE AREA, MONITOR RESULTS, AND ACT ACCORDINGLY.
1. Apply acid-based cleaner using a soft nylon bristle
brush. Allow to remain on the surface as long as
determined by testing. DO NOT EXCEED 5-7 MINUTES.
2. Rinse the surface thoroughly with clean, clear
water using pressure between 400 and 600 psi.
Direct spray downward as noted above. Monitor interior spaces and contain water from rinsing operation so as not to
flood building interior.
3. If efflorescence appears, clean a second time with
a hydrofluoric acid-based cleaner, followed
immediately by rinsing with cold water.
END OF SECTION
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