Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
- 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.
- Dutchman repair is sometimes recommended for large spalls or spalls that would be visually detract= ing.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- Sample Stone Repair:
- 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.
- If samples are unsatisfactory, Contractor shall make the needed modifications and prepare new samples until they are satisfactory.
- 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.
- 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
- 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.
- 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.
- 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
- 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.
- Polymer Admixture (for Setting Dutchman) such as "Laticrete 3701 or 4237 Grout and Mortar Admixture" (Laticrete International, Inc.), or approved equal.
- Metal attachments for setting stone Dutchman:
- All wire, pins, anchors, and bars shall be stainless steel, Type 302 and 304.
- Provide anchors as follows:
- 1/8" diameter round stock, stainless steel wire with turned-up ends for small veneers.
- 1/4" or 3/8" diameter round stock, stainless steel rod for direct pinning and drop dowels.
- 1" wide, 1/8" thick, stainless steel, flat strap anchors for larger panels.
- 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.
- All attachments shall be fastened by mechanical locking, in addition to appropriate adhesives and mortars.
- 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.
- Pigments for altering the color of cement: All pigments shall be alkali proof, non-fading, and of synthetic iron oxides.
- 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.
- Joint tools
- Wood wedges
- Spray bottle
- Protection: Contractor shall take whatever precautions are necessary to protect the existing building from damage resulting from work under this section.
- Surface Preparation: Cut existing spalls to form rectangular losses with square corners, minimum 2" thickness.
3.02 ERECTION, INSTALLATION, APPLICATION
- 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.
- 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.
- "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.
- 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.
- 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.
- 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.
- Protect the limestone during the process of stone restoration. Any mortar accidentally splashed onto existing limestone shall be wiped and rinsed with water.