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Historic Preservation - Technical Procedures

Spectitle:

Reinforcing Loose Terra Cotta Units And Patches

Procedure code:

0421403R

Source:

Us Custom House/Portland, Or - Gsa/Facilities Support Ctr

Division:

Masonry

Section:

Terra Cotta Unit Masonry

Last Modified:

11/13/2012

Details:

Reinforcing Loose Terra Cotta Units And Patches



REINFORCING LOOSE TERRA COTTA UNITS AND PATCHES


THIS PROCEDURE SHOULD BE PERFORMED UNDER THE DIRECTION OF AN
HISTORICAL ARCHITECT OR ENGINEER TO DETERMINE THE MOST EFFICIENT
AND LEAST DESTRUCTIVE MANNER FOR EXECUTING THE WORK.  APPROVAL
FROM THE REGIONAL HISTORIC PRESERVATION OFFICER IS REQUIRED.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on installing bent wire
         armatures or studs in terra cotta to additionally
         reinforce and anchor existing patches that are more than
         1/2" thick, or any patch which is approximately fist
         size.

    B.   This procedure requires substantial intervention and is
         only to be used to secure large patches to already
         damaged terra cotta surfaces.  If not properly anchored,
         large patches are particularly vulnerable to failure and
         separation due to weight, thermal expansion and bond
         failures.

    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 MANUFACTURERS

    A.  Sika Corporation
         usa.sika.com



    B.  Abatron, Inc.
         www.abatron.com


2.02 MATERIALS

    A.   Stainless steel or bronze wire armature, or threaded rods
         and bolts.  Threaded rods shall be sized according to the
         need and loading requirements.  Consult with structural
         engineer and RHPO.

         1.   Wire shall be 12-gauge or heavier.

         2.   Stainless steel shall be AISI Type 316.

         3.   The use of a wire armature or threaded rods shall
              be determined by size, depth and thickness of patch
              being stabilized.  To be determined by structural
              engineer and RHPO.

    B.   Moisture insensitive, structural epoxy or polyester resin
         adhesive as recommended by adhesive manufacturer (Sika
         Corporation, Abatron, Inc., or approved equal).  

    C.   Acrylic-cement finish.

2.03 EQUIPMENT

    A.   Masonry drill with diamond tipped coring bits.

    B.   Electric drill with mixing paddle to pre-mix epoxy
         adhesive.

    C.   Clean pail in which to mix epoxy adhesive.

    D.   Pressure-injection equipment as may be required.

    E.   Mixing nozzle:  As recommended by adhesive manufacturer,
         the resin components may be automatically mixed by a
         nozzle that is secured to the component cartridges.


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Holes:

         1.   The drill holes should be sized according to the
              wire or rod used.  Typically, the hole shall be no
              greater in diameter than 1/8-inch or 1/4-inch
              (depending on the adhesive used) larger than the
              pin to be embedded, and ten to fifteen bar
              diameters deep.  

         2.   Drill shall be non-impact type rotary drill with a
              masonry bit.

         3.   Depth of hole shall be sufficient to reach sound
              backing material.

         4.   Space wire armature reinforcing at approximately
              2-inches on center, arranged in a grid or mesh where
              applicable, or as recommended by structural engineer.

         5.   Clean holes with high pressure air.

    B.   Protection:  Protect surfaces around holes from contact
         with adhesives.  Use petroleum jelly, modeling clay or
         polyethylene sheets as required.

    C.   Installation:

         1.   Verify the rod length as appropriate for the depth.

         2.   If using automatic pressure-injection equipment,
              resin shall be automatically measured and mixed in
              the mixing nozzle.  

         3.   If mixing by hand, mix each component by volume as
              directed by manufacturer into clean pail.
              Components shall be used straight, without any
              additives.  Mix thoroughly for time specified by
              manufacturer with low-speed drill (400-600 rpm)
              fitted with appropriate paddle.  Blend until
              uniform color is achieved.

         4.   Pack or place the resin into holes.

         5.   Slowly insert the wire armature or threaded rod
              into the resin to the full depth of the hole.
              Countersink head of rods.

         6.   Do not disturb the anchor until the adhesive has
              cured.  Follow manufacturers instructions.

         7.   No gaps shall be visible between the rod and the
              masonry.

    D.   Plug counter-sunk holes and build-out face of damaged
         patches as required flush with surrounding surfaces using
         patching mortar as described in HBPP procedure 04214-01-R,
         "Patching Small Holes, Minor Chips and Spalls in Terra Cotta".

3.02 ADJUSTING/CLEANING

    A.   Immediately remove spills and excess adhesive with
         absorbent material and flush with water.  

    B.   Uncured material can be removed with solvent as
         recommended by adhesive manufacturer.  

    C.   Do not allow excess material to cure as cured adhesive
         can only be removed mechanically.  

3.03 PROTECTION

    A.   Apply one coat colored masonry acrylic-cement finish to
         protect and repair damaged surface areas.

    B.   Apply this protective, coloring, coating to existing old
         patch areas where the color does not match the terra
         cotta.

                         END OF SECTION
 


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