Sealing Terra Cotta
- CSI Division:
- Division 4- Masonry
- Terra Cotta Unit Masonry
- Last Modified:
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.
SEALING TERRA COTTA
A. This procedure includes guidance on sealing terra cotta units which have lost their surface glaze.
B. 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
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).
A. American Society for Testing and Materials (ASTM),
A. ProSoCo, Inc.
A. Terra Cotta Sealing Materials: One-part, opaque, water base exterior masonry coating, containing silicone resin binders, that has excellent UV stability and allows at least 90% moisture vapor transmission based on ASTM E96, such as "BMC II Breathable Masonry Coating" (ProSoCo, Inc.), or approved equal. NOTE: Test all colors and receive approval from RHPO that color match is acceptable.
B. Water: Clean, free of oils, acids, alkalis and organic matter.
1. Protect persons, motor vehicles, surrounding surfaces of building whose masonry surfaces are being restored, building site, and surrounding buildings from injury resulting from masonry restoration work.
2. Erect temporary protection covers over pedestrian walkways and at points of entrance and exit for persons and vehicles which must remain in operation during course of masonry restoration work.
3. Protect sills, ledges, windows, and projections from sealing material droppings.
3.02 ERECTION, INSTALLATION, APPLICATION
A. Areas to be sealed: Areas to be sealed are only patches of the terra cotta units which have lost their surface glaze. Lightly brush spalled areas to remove loose material and glaze that has failed but not fallen from face of unit.
B. Clean terra cotta with sponge and clean water before sealing:
C. Prime areas to be sealed with specified primer using brush or roller application, strictly adhering to manufacturer's recommendations. Promptly remove all primer from surrounding surfaces. Test small areas of terra cotta and gain approval of manufacturer's representative and Contracting Officer before proceeding. Allow primer to dry 10 hours before applying masonry coating.
D. Apply breathable masonry paint in two coats, strictly adhering to manufacturer's recommendations. Brush apply first coat, wait 24 hours and brush apply second coat. Color shall match adjacent terra cotta units. Test small area of terra cotta and gain approval of manufacturer's representative and Contracting Officer before proceeding.