Insulating Glass: Problems and Prevention

The most obvious indication of failure of an installed insulating glass (IG) unit in a window or door is permanent visual obstruction due to a milky-white fog or film on the interior surfaces of the glass (surface numbers two or three in dual-pane IG) due to moisture or chemical deposition. Note that the keyword in the definition of IG failure is “permanent.” The IG unit cannot be classified as a failure if it fogs only during extremes, such as when the temperature falls to –23 C (–10 F) and remains clear the rest of the time.

Problems

Permanent fogging of an IG unit can be caused by hermetic seal failure, which allows intruding water vapor to overcome the dehydration capacity of the desiccant and condense on the inside glass surfaces. Fogging can also be due to film deposits left on insufficiently washed glass (e.g., residue of cleaning solution, adhesive or oils from excessive handling), by the accumulation of the products of chemical interaction between volatiles released from components (spacers, sealants, muntin bars or grilles, desiccant, paints) or component incompatibility (e.g., glazing sealant vs. IG sealant).

Seal failure can also cause loss of inert gas infill, which degrades thermal performance. Windows without the proper safeguards to keep water from puddling around the perimeter seals will thus fail sooner.

Excess heat due to direct sun exposure, especially in south-facing windows, can also degrade seals or spacers. Daytime heating followed by nighttime cooling causes the panes to expand and contract, softening and weakening the seals until they compromise the seal’s adhesion or develop cracks that admit moist air. 

Other common causes of seal and/or spacer failure are fabrication-related, such as cracked glass due to excessive edge pressure or poor edge quality from cutting, voids or excessive air pockets in the sealant bead, poor corner fill, poor spacer/glass alignment, desiccant that has been left exposed too long before sealing, poor mix of sealant and damaged low-E coating.

Although rare, with a failure rate of about 1 percent after 10 years when properly installed, such permanent failures are highly visible, require window replacement and are potentially detrimental to the reputation of the fabricator.

Prevention

To help prevent such problems, it is important that IG fabricators and shop floor team leaders understand what material or fabrication process steps tend to harbor the root causes of degradation, as well as the design considerations that minimize edge seal failure based on existing seal technology. They should also understand proper selection and use of compatible sealants, desiccants, spacers, in-fill gases, glass coatings, grilles or muntins, and other components, as well as the elements of testing, packaging, shipment and glazing of IG units.

To provide guidance for effective quality control, improve the likelihood that products will pass certification testing (as often required by AAMA and NFRC standards, codes and Energy Star) and avoid future failures, FGIA sponsors an IG Fabricator Workshop. The next of these — the first since the COVID-19 shutdown — will be held this coming November, with specific date and location to be announced. Since its launch in 2016, this workshop has hosted more than 300 IG industry practitioners, leading them through the aspects of IG fabricating and testing in classroom sessions and hands-on demonstrations to discover best practices for cleaning, cutting and handling glass, desiccants, sealants, gas fill, frost point testing and much more. 

Specifically, the program helps in the development and maintenance of an effective Quality Management System by covering:

• Insulating glass basics (design, energy performance and glazing guidelines)
• Glass receiving, cutting and washing
• Handling glass safely
• Characteristics and placement of rigid and flexible spacers
• Use of muntins and grids
• Desiccants and desiccant matrix
• Sealants (types, proper selection and application, and adhesion to glass)
• Gas filling

Third-party product certification to ASTM E2190, which includes laboratory testing for dew/frost point, accelerated cycling between extremes of temperature/moisture/UV exposure, and gas fill durability

A previous participant of a past workshop said, “The hands-on portion is awesome. Being able to take what was learned in a presentation and then apply it in real life was really effective.”

Plan now to attend the post-COVID resumption of this workshop. Watch for scheduling details at FGIAonline.org/IGworkshop.