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The rise of the blue roof fire rated silicone sealant
Crystal-clear Protection: Using waterproofing to safeguard against concrete corrosion
Using plenum barriers to comply with sound isolation requirements
Effective sound control of doors
Structural silicone glazing (SSG) continues to grow in popularity for its aesthetic and performance characteristics. Its superior thermal performance compared to captured systems allows designers to enable compliance with more stringent energy standards and code requirements while reducing sightlines between glazed units.
In an SSG application, the silicone sealant bonding the unit to the framing is typically a high-performance, multi-component adhesive designed to function as the structural attachment between noted components, specifically formulated for its adhesive and curing properties which also serves as a primary seal against air and water infiltration. ASTM C1401, Standard Guide for Structural Sealant Glazing, provides useful information related to the design and installation of SSG applications. Additional structural silicone guidelines and performance criteria are available from the American Architectural Manufacturer’s Association (AAMA), the Glass Association of North America (GANA), and the American Society of Civil engineers (ASCE).
Curtain wall systems that utilize structural silicone glazing are typically configured as either two- or four-sided SSG assemblies. Since SSG performance is dependent on the joint configuration and the integrity of the sealant’s bond to transfer loads imposed on (or by) the infill to the framing, several factors must be considered when designing and installing SSG systems to better ensure long-term performance. While field glazing can be successfully performed with the appropriate structural sealant, shop glazing of SSG systems is strongly recommended due to the improved environmental and quality controls offered by this fabrication method.
Whether field or shop fabricated, one quality control measure to confirm the integrity and consistency of the structural sealant application is to deglaze representative assemblies—deglazing representative assemblies also assists in developing protocols for infill replacement should the infill be damaged in-service. Inspection during deglazing should include verification that the structural sealant glueline (thickness) and bite (bond width) satisfy the design requirements. Evaluation of the adhesion of the structural sealant to the infill and frame can also be performed as part of this evaluation, as well as visual examination of the sealant for any anomalies such as the presence of bubbles, entrapped air, or other detrimental variations in the sealant. Other relevant observations during the deglazing process can include verification that approved components (i.e. gaskets, other sealants, cleaners, primers, spacers, setting blocks, etc.) are properly installed.
Deglazing operations should be conducted at the start of fabrication to help ensure/establish quality workmanship, with periodic inspection throughout the fabrication process to confirm sustained quality. ASTM C1401 recommends quality control (QC) deglazing at a rate of one unit in the first 10 produced (1/10), one in the next 40 (2/50), one in the next 50 (3/100), and one in every 100 thereafter. If any deglazed units reveal deficiencies or other conditions of concern, additional units glazed on the same (or previous) date may be deglazed to help identify if the quality issue or concern is an isolated or repeated defect. Representative examples of issues encountered by the authors during past deglazing efforts are illustrated above.
Dana Landis, PE, is an architectural engineer and senior associate with the Philadelphia office of Wiss, Janney, Elstner Associates (WJE), specializing in building science and building enclosure consulting and commissioning. She can be reached at dlandis@wje.com.
Jeffrey Sutterlin, PE, is an architectural engineer and associate principal with Wiss, Janney, Elstner Associates’ (WJE’s) office in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. He can be reached at jsutterlin@wje.com.
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect that of The Construction Specifier or CSI.
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