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.
THE APPROPRIATE METHOD OF SEALING JOINTS IS THE PROPER REPOINTING WITH COMPATIBLE HISTORIC MORTAR MIX (SEE 04100-03-S AND 04250-02-R FOR GUIDANCE). UNDER CERTAIN CONDITIONS, HOWEVER, SELECTIVE USE OF SEALANT MAYBE WARRANTED TO ADDRESS EXTREME THERMAL MOVEMENT OR OTHER LOCATION-SPECIFIC CONDITIONS. A DECISION TO SUBSTITUTE SEALANT FOR MORTAR SHOULD BE BASED UPON SITE-SPECIFIC ANALYSIS TO IDENTITY DEFICIENCY CAUSES AND APPROPRIATE SOLUTIONS.
- This procedure includes guidance on removing deteriorated sealant from horizontal limestone joints and recaulking with a waterproof joint sealant. This procedure specifically applies to exterior limestone window sills, balustrades, balconies and cornices, although use on other horizontal surfaces may be appropriate.
- 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).
- American Society for Testing and Materials (ASTM) www.astm.org
- Joint sealant: Multi-part, non-sag urethane sealant conforming with ASTM C290, Type M, Grade NS, Class 25.
- Joint primer: Provide as recommended by sealant manufacturer.
- Backer rod: Round, closed cell, polyethylene foam backing rod; should be compatible with sealant; use as recommended by sealant manufacturer.
- Stiff natural fiber or nylon bristle brushes
- Striking hammer or "No-bounce" hammer
- Joint chisel
3.01 ERECTION, INSTALLATION, APPLICATION
- Rake out old sealant or mortar from joints by hand using a hammer and chisel. Rake to expose sound mortar. See also 04520-02-R for guidance on raking out joints. NOTE: DO NOT USE MECHANICAL METHODS TO CUT OUT JOINTS, DUE TO THE HIGH PROBABILITY OF DAMAGING THE STONE. TAKE CARE NOT TO CHIP OR SPALL EDGES OF ADJACENT STONE.
- Remove loose dirt and debris from the joint using a stiff bristle brush or vacuum.
- Prime joint surfaces as recommended by the sealant manufacturer. Protect adjacent surfaces from spillage or spattering of sealant.
- Insert backing rod to a depth equal to 1/2 the width of the joint.
- Fill joint with sealant. Tool joint within 10 minutes of placing. Finish joint level with the stone surface.
- Remove excess sealant from the stone surface immediately.