FGIA Analysis September 2020

July 27th, 2021 by Nathan Hobbs

IG Failures: With a Handful of Culprits, QC and Proper Guidance Make It Clear

By Margaret Webb

While many in the industry understand what an installed insulating glass unit (IGU) in a window or door is, fewer know what unit failure looks like. An IGU is considered to have failed when it exhibits permanent material obstruction of vision through the unit due to accumulation of dust, moisture or film on the internal surface of the glass, resulting in a milky white fog. Such fogging has two possible sources:

First is moisture fogging due to seal failure, which occurs if the perimeter seal of the unit is broken or compromised. Intruding water vapor quickly overcomes the dehydration capacity of the desiccant contained within the tubular spacer bar, and the excess moisture condenses on the inside of glass surfaces. Seal failure can also cause loss of inert gas infill, which degrades thermal performance. Second is chemical fog, which is caused by outgassing of products through the interaction of incompatible or damaged components and materials.

Three Primary Suspects

Among the leading causes for seal failure of installed IGUs is seal break down from excessive exposure to water. Without proper drainage, a window will allow water to puddle around the seals, slowly degrading them. Moisture will enter the cavity space as the window thermally expands and contracts. A glazing pocket incorporating setting blocks to lift the bottom edge of the IG unit out of the water path and weep holes in the glazing pocket can help prevent this. Another leading cause includes excess heat, which is usually due to direct sun exposure. Heat causes the panes to expand and contract, softening seals until they crack. Lastly, there is old age, as even the most elastic seal can break down over time and become brittle, eventually failing.

Other Culprits

Other common causes of seal and/or spacer failure are fabrication related, such as: voids, skips, or excessive air pockets in the sealant bead; poor corner fill; poor spacer/glass alignment; desiccant that has been left exposed to ambient air too long before sealing; and poor mix of sealant.

Film deposits, other than condensed water vapor due to seal failure, can be caused by:
• Component incompatibility or quality issues with the component;
• Cutting oils or cleaning solvents left after glass washing;
• Internal components, particularly muntins, which can introduce another source of contamination traceable to paints or vinyl materials (also, mishandling of muntins can leave dirt and oily residue from hands or solvents);
• Particulate residue from spilled desiccant material;
• Dirty glass, caused by dirty cleaning water, insufficient rinsing of the glass prior to assembly, poor workmanship, poorly maintained equipment or improper handling of the unit during fabrication.


IG manufacturers can minimize the frequency of such in-service failures as well as forestall premature aging by observing proper fabrication procedures and applying effective quality control.

To provide guidance for proper material selection and IG fabrication that will help avoid these problems, FGIA has published the Preventing Insulating Glass Failures Manual (IGMA TM-4100-03). FGIA also offers its Insulating Glass Manufacturing Quality Procedures Manual (IGMA TM-4000-02(07).

Lastly, November 10-12, an IG Fabricator Workshop is tentatively scheduled to be held at the Intertek Facility in Plano, Texas, just outside Dallas. Since its launch in 2016, this workshop has hosted more than 300 industry practitioners, leading them through the most important aspects of fabricating and testing IG units.

Margaret Webb is the Glass Products and Canadian Industry Affairs Director of the Fenestration Glazing Industry Alliance with offices based in Chicago and Ottawa, Ontario.

To view the laid-in version of this article in our digital edition, CLICK HERE.

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