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Historic Preservation - Technical Procedures

Spectitle:

General Cleaning Of Exterior Limestone

Procedure code:

0446003R

Source:

Hsr - Departmental Auditorium Bldg/Wash, Dc - Grier, Brown..

Division:

Masonry

Section:

Limestone

Last Modified:

10/26/2012

Details:

General Cleaning Of Exterior Limestone



GENERAL CLEANING OF EXTERIOR LIMESTONE


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


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on the removal of
         surface dirt and environmental pollution on exterior
         limestone.  GENERALLY, THIS WORK SHOULD BE ACCOMPLISHED
         BY AN EXPERIENCED CONTRACTOR.

    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).

    C.   For precautions relating to pressure washing, see 04510-04-S.

PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.  ProSoCo, Inc.
         www.prosoco.com
         
2.02 MATERIALS

    A.   Limestone (unpolished):  Sodium hydroxide, (pH 14), undiluted
         such as "Sure Klean Limestone Prewash" and "Sure Klean
         Limestone Afterwash" (ProSoCo, Inc.), or approved equal.

            1. For heavy high pollution stains, an alkaline-based prewash such as "Sure Klean 766 Limestone & Masonry Prewash" or equal, follow             manufacturer's instructions including rinse cycle.

            2. Followed up with "Sure Klean Limestone & Masonry Afterwash, Restoration Cleaner, or Limestone Restorer" or equal, as per             manufacture's instructions.

    B.   Clean, potable water (heated to a temperature effective
         and tested for cleaning procedure and approved by RHPO).

2.03 EQUIPMENT

    A.   Pressure water rinsing equipment (measuring between 100
         and 400 psi for low-pressure; between 400 and 1000 psi for
         medium pressure).

    B.   Fan-type spray tips (15 -45 degree fan spray)

    C.   Stiff fiber-bristle brushes

    D.   Plastic spatula


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 from coming in contact
              with the cleaning materials and run-off.

         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
              repoint mortar joints and caulk gaps around window & door openings, as required to prevent water and
              cleaning solutions from penetrating deeply into the
              wall.

         3.   Clean the limestone working from bottom to top.

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.  DO NOT PROCEED UNTIL AN ACCEPTABLE CLEANING
    OPERATION HAS BEEN APPROVED AND FULLY DOCUMENTED.

    NOTE:  DO NOT TREAT THE SURFACE WITH ACID CLEANER MORE THAN
    ONCE.

    A.   Pre-wet limestone surface using a low pressure wash
         (between 100 and 400 psi).

    B.   Apply a heavy coating of limestone pre-wash using a soft,
         nylon bristle brush.  Follow manufacturer's applications
         instructions.

    C.   Allow to stand for one hour or as long as determined by
         testing.

    D.   Thoroughly rinse the surface using high pressure water
         (between 800 and 1000 psi).  Rinse until no sudsing
         remains.  

         1.   Rinse all corners, moldings, and interstices to
              remove all traces of chemical without damaging
              surrounding materials.

         2.   Rinse water should be heated to 150-180 degrees Fahrenheit or
              as determined most effective during testing.

    E.   While surface is still wet from rinsing off pre-wash,
         apply limestone afterwash with a soft, fiber bristled
         brush.  

         1.   Dilute limestone afterwash with as much water as
              determined effective during testing.

         2.   If surface has begun to dry, re-wet before applying
              afterwash.

         3.   Cover all corners, moldings, and interstices of the
              limestone.

    F.   Allow to stand for 3-5 minutes or as long as determined
         by testing.

    G.   Thoroughly rinse the surface using high pressure water
         (between 400 and 1000 psi), with a water flow of 6-8 gallons per minute.

         1.   Rinse all corners, moldings, and interstices to
              remove all traces of chemical without damaging
              surrounding materials.

         2.   Heat rinse water to a temperature determined most
              effective during testing.

                         END OF SECTION
 


limestone cleaning, exterior limestone cleaning