3.2 Specify an appropriate sealant application method
When performing field installation of SSG, preparation of the new or existing substrates for new structural sealant varies by manufacturer and typically requires the sealant manufacturer’s project-specific approval and validation through project-specific adhesion testing.
If the new and existing structural silicone products are from the same sealant manufacturer, preparation of the substrate typically involves removal of the existing cured sealant down to a thin film, onto which the new sealant is adhered (Figure 6). With manufacturer confirmation and project-specific testing, the thin film can provide a reliable surface for adhesion and avoid the need for additional surface cleaning and priming of the raw frame surface.
There are two primary methods of installing the structural sealant for field installed SSG applications. The first option is to install the sealant from the building interior after the new IGU is placed in the opening and secured with temporary stops; installers typically use a thin flexible nozzle fully inserted into the joint pocket to ease installation and ensure complete filling of the joint (Figure 7). This option is more reliable since a worker on the exterior can provide continuous inspection of the sealant installation using a flashlight, and flag bubbles and voids for immediate repair as the structural sealant is being installed.
As a second option, some installers may default to a ‘blind’ or ‘smash’ seal, where workers apply sealant to the existing prepared frame and then press the IGU into place (Figure 7). Blind seals offers neither ability for the installer to gage the continuity, fill, or adhesion of the installed joint, nor interior access to the sealant joint for adhesion pull tests and other quality control or quality assurance measures.
On hot summer days, the sealant may partially or fully skin over before the IGU is pressed into place resulting in incomplete bond and potentially loss of structural attachment. Blind seals should not be used, and if absolutely required (e.g. at spandrel panels where interior access is not possible) they demand elevated quality assurance and frequent quality control testing (i.e. full removal of installed IGUs—referred to as deglazes—to validate success of installation methods).
Always follow the manufacturer’s installation procedures and quality control requirements and use only proven techniques that have been validated through successful quality assurance documentation and quality control testing. Many installers, while very knowledgeable and practiced with installation of shop fabricated SSG systems, have experience with field installation of SSG limited to situations where a small number of glass lites are replaced (e.g. limited glass replacement due to breakage during construction and leave-out panels to accommodate access equipment anchor points) and quality control and quality assurance measures may be an afterthought or not sufficiently robust.
The authors have seen the results of quality control deglazes on buildings where experienced installers were shocked to see the unintended vulnerabilities of less-than-ideal SSG reglazing procedures on field-installed SSG systems they have constructed. The margin between success and failure can be unnoticeable even to the experienced installer’s eye due to the inherent shortcomings of field SSG installations that are not representative of factory SSG installations.
3.3 Specify a robust quality control program
Regardless of the quantity and overall scope of a field SSG replacement project, the designer should specify a robust field quality control program that evaluates if the field installed SSG joints meet or would be expected to meet the specified performance criteria (i.e. through evaluation of primary joint characteristics: material strength, joint geometry, continuity, cure, and adhesion).
A robust quality control and quality assurance program should include tests before, during, and after SSG installation, which may include the tests below as applicable. Refer to the sealant manufacturer literature for product specific testing requirements which often indicate required quantities and frequency of testing necessary to secure the manufacturer’s warranty.
Pre-Installation:
Material Specification (ASTM C864)
Material Compatibility (ASTM C1087)
Adhesion (ASTM C1135)
Installation:
Skin-Over Time (ASTM 1401, Appx. X3)
Elastomeric Characteristics of a One-Component Sealant (ASTM C1401, Appx. X4)
Butterfly Test (ASTM C1401, Appx. X5)
Snap Test (ASTM C1401, Appx. X6)
Post-Installation:
Pull Adhesion Test (ASTM C1401, Appx. X2)
Deglaze Test (Typically Manufacturer Requirement)
Air Infiltration Test (ASTM E783)
Water Penetration Test, Chamber (AAMA 503, ASTM E1105), Nozzle (AAMA 501.2)
Load Testing (ASTM C1392)
the installers shall be trained in the proper installation of dow 795 structural silicone