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Historic Preservation - Technical Procedures

Spectitle:

Dutchman Repair Of Limestone

Procedure code:

0446011R

Source:

National Capitol Region Specifications - Gen Accounting Off

Division:

Masonry

Section:

Limestone

Last Modified:

07/30/2013

Details:

Dutchman Repair Of Limestone



DUTCHMAN REPAIR OF LIMESTONE


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on the repair of damaged
         limestone using a dutchman.  As used here, the term
         "Dutchman" refers to any new or salvaged stone fitted
         into the existing facade stone. New stone shall match
         existing.

    B.   Dutchman repair is sometimes recommended for large spalls
         or spalls that would be visually detract= ing.

    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 Precaution= s

         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 SUBMITTALS

    A.   Sample Stone Repair:

         1.   Reattach stone fragments and patch stone at
              locations selected by the Contracting Officer using
              methods specified. Provide one sample each for
              materials to be used.

         2.   If samples are unsatisfactory, Contractor shall
              make the needed modifications and prepare new
              samples until they are satisfactory.

         3.   The samples accepted by the Contracting Officer
              shall serve as the standard for the entire job.
              They shall be marked and left unpointed until all
              other pointing is completed.

         4.   The Foreperson responsible for the respective work
              shall be present at the sample work. Samples shall
              be executed by the same individuals performing the
              work.

1.03 QUALITY ASSURANCE

    A.   Contractor: A skilled firm with not less than five (5)
         years experience in masonry repointing and restoration.
         The Contractor shall be required to submit references for
         five (5) successfully completed projects of similar
         nature.

    B.   Work Standards:  Repointing basic reference and standard
         for stone repointing shall be National Park Service
         Preservation Briefs: 2 Repointing Mortar Joints in
         Historic Brick Buildings, by Robert C. Mack AIA, de Teel
         Patterson Tiller, and James  S. Askins for any aspect of
         masonry repointing work not herein specified.

    C.   Source of Material: Obtain materials for stone
         restoration from a single source for each type of
         material required, to ensure match of quality, color,
         pattern, and texture.

1.04 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements:  Perform work only in dry and
         otherwise favorable weather conditions. Protect repaired
         masonry against freezing or excessively rapid drying for
         at least 48 hours after being laid; no masonry shall be
         laid when temperature is below 32 F on a rising
         thermometer or below 40 F on a falling thermometer.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Laticrete International, Inc.
         www.laticrete.com

    B.   Sika Corporation
         http://usa.sika.com

2.02 MATERIALS

    A.   Polymer Admixture (for Setting Dutchman) such as
         "Laticrete 3701 or 4237 Grout and Mortar Admixture"
         (Laticrete International, Inc.), or approved equal.

    B.   Metal attachments for setting stone Dutchman:

         1.   All wire, pins, anchors, and bars shall be
              stainless steel, Type 302 and 304.

         2.   Provide anchors as follows:

              a.   1/8" diameter round stock, stainless steel
                   wire with turned-up ends for small veneers.

              b.   1/4" or 3/8" diameter round stock, stainless
                   steel rod for direct pinning and drop dowels.

              C.   1" wide, 1/8" thick, stainless steel, flat
                   strap anchors for larger panels.

         3.   The quantity of individual attachments shall not be
              less than two attachments for small dutchman, and
              one attachment every two square feet for larger
              panels.

         4.   All attachments shall be fastened by mechanical
              locking, in addition to appropriate adhesives and
              mortars.  

    C.   Adhesives for attaching anchors and for direct pinning:
         Where permitted, anchors may be held in place with high
         modulus, high strength, moisture insensitive, epoxy
         adhesive. Adhesive shall be two-component 100% solids,
         epoxy resin system with a viscosity similar to petroleum
         jelly "Sikadur 31 Hi-Mod Gel" (Sika Corporation), or
         approved equal.

    D.   Pigments for altering the color of cement:  All pigments
         shall be alkali proof, non-fading, and of synthetic iron
         oxides.

    E.   Water: Clean and free of amounts of oils, acids, alkalies, salts, organic materials, or other substances
         that may be deleterious to mortar or any metal in the
         wall.

2.03 EQUIPMENT

    A.   Trowel

    B.   Hawk

    C.   Chisel

    D.   Hammer

    E.   Joint tools

    F.   Wood wedges

    G.   Spray bottle


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:  Contractor shall take whatever precautions
         are necessary to protect the existing building from
         damage resulting from work under this section.

    B.   Surface Preparation: Cut existing spalls to form rectangular losses with square corners, minimum 2"
         thickness.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   Mortar for setting limestone Dutchman shall be mixed in
         a ratio of one part by volume white portland cement and
         three parts by volume sand, tempered to a workable
         consistency with a polymer admixture.

         1.   The use of Laticrete 3701 shall produce the
              equivalent of high strength "thick set" mortar.
              Limestone must be temporarily held in place with
              wood wedges or other means until the mortar has
              sufficiently set.

         2.   "Thinset" mortars for special conditions shall
              employ Laticrete 4237, or approved equal. It can be
              used when the mortar bed is less than 3/8" thick to
              produce an initially tacky mortar exhibiting high
              strength properties when set.

    B.   Dutchman shall be fastened with stainless steel wire,
         pins, and anchors, as necessary, designed to facilitate
         mechanical locking and to prevent possible slippage of
         the stone. The metal fasteners shall be positioned
         without weakening the stone in any way.  See also 04460-
         13-R for guidance on resetting limestone.

    C.   Cement mortar containing "Laticrete" latex emulsion
         additives, or approved equal, shall be used for all
         setting purposes. All insertion shall be fully dressed on
         all sides, and carefully fitted to the patch opening,
         with an allowance of not more than 1/8 inch buttered joint
         between front edges. Undercutting shall not weaken the
         stone in any way. The joints between new and old work
         shall be finished to match the color and texture of the
         stone.  See 04520-02-R for guidance on repointing.

    D.   The surface of the new stone shall be dressed to resemble
         the appearance of the adjoining stone by an approved
         method. All surface dressing of new work shall be done
         before the stone is set.

    E.   Protect the limestone during the process of stone restoration. Any mortar accidentally splashed onto
         existing limestone shall be wiped and rinsed with water.

                         END OF SECTION
 


limestone repair, dutchman repair, salvage stone