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Historic Preservation - Technical Procedures

Spectitle:

Removal Of Waterproof Coating From Granite

Procedure code:

0446504R

Source:

Federal Building/Courthouse, Sioux Falls, Ia

Division:

Masonry

Section:

Granite

Last Modified:

06/14/2012

Details:

Removal Of Waterproof Coating From Granite



REMOVAL OF WATERPROOF COATING FROM GRANITE


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on how to remove a
         surface applied waterproof coating which has begun to
         discolor and flake-off due age, poor penetration or
         improper application.

    B.   Safety Precautions:

         1.   Workers shall be provided with protective clothing
              including full head and face protection and noise
              protection.

         2.   Helmet shall be "air-line" type to maintain
              positive air pressure inside helmet to prevent the
              ingress of dangerous abrasive dust.

    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).


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Fine abrasive - type to be determined by field testing
         completed prior to actual cleaning.  Possible abrasives
         include talc, ground nut shells or egg shells, both
         angular and smooth sands depending on cutting edge
         required to remove deteriorated coating.

    B.   Water - clean, clear, potable.  

2.02 EQUIPMENT

    A.   Air compressor (with pressure gauge)

    B.   Appropriate nozzle - long venturi nozzle for flat
         surfaces with consistent soiling conditions; short
         straight nozzles for detailed areas.  Shapes to be
         determined by field testing.  Nozzle should be type that
         allows for different modes of operation, abrasive and
         air, abrasive and water, air only and water only to allow
         greater control by operator.

    C.   High pressure water lance (maximum pressure not to exceed
         400 psi.)


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Using low pressures (60 to 80 psi at the compressor),
         apply stream of abrasive/water mixture to wall surface
         being cleaned.  Begin with lowest pressure and softest
         abrasive determined appropriate by pretesting.

         1.   Maintain minimum 12" from the surface of the stone
              and do not allow stream to stay in one spot for
              more than a few seconds.  

         2.   Do not allow direct blasts at mortar joints.  

         3.   Check work frequently and stop cleaning as soon as
              coating has been removed.  

         4.   Reduce air pressure if damage to stone occurs.

         5.   To avoid "gun-shading" do not rush through work,
              and maintain steady, even control.

    B.   After surfaces have been cleaned, wash surfaces to remove
         all traces of slurry and spent abrasives.  Use a low-volume,
         high-pressure water lance, with pressure not to
         exceed 400 psi at the compressor.  Use hand-sprays as
         necessary on small scale details.

                         END OF SECTION
 


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