Spacers, Sealants and Machines
How to Sort Through the Selection Process
by Jim Plavecsky
When it comes to fabricating an insulating glass (IG) unit that will stand the test of time, the choice of sealant is absolutely critical. Oftentimes, fabricators are so interested in optimizing the thermal properties of the unit, they forget about the durability. An IG unit that has the best U-value and condensation resistance is still no good to a consumer if it lacks the capability to provide long term weather resistance and argon retention.
Look at the Attributes
When it comes to building in durability, the sealant selection and application is just as important as the type of spacer employed. There are five key attributes of sealants that must be studied before deciding which one to choose. These are adhesion, moisture vapor transition rate, rate of argon permeability, weather resistance and process characteristics on the particular application equipment to be used.
Adhesion is critical because the sealant must bond tenaciously to both the spacer and the glass while enduring temperature extremes and weather exposure. They must also endure constant flexing as the unit undergoes temperature changes, barometric pressure changes and
windload. There are many new warm-edge spacers on the market and new options seem to pop up every year. When choosing a warm-edge spacer or any spacer for that matter, it is important to check with both the spacer suppliers and sealant suppliers to see if the particular spacer chosen has been tested with the particular sealant with which it is to be used. Look for test data that includes both adhesion and weather endurance. Ideally, the spacer-sealant combination has been tested to the new Harmonized Insulating Glass Standard
(HIGS) for long term IG endurance.
Moisture Vapor Transmission Data
Moisture vapor transmission data is available from the various sealant suppliers. Testing is conducted to determine that rate at which moisture vapor passes through a given sealant membrane. The lower the rate the better, because the desiccant employed within the spacer must be able to keep up over the years by absorbing this moisture vapor as it enters the unit. When the desiccant is all used up, the unit will fog. When reviewing data, it is important to make sure that you are comparing “apples to apples” as different sealant suppliers may be reporting results in different units.
Argon permeability data is one area which many fabricators grossly underestimate in terms of importance. I often hear remarks like, “I simply don’t guarantee how long the argon will stay in. We put it in initially, but we make no claims as to how long it will stay there.” However, remarks such as these show that the fabricator perhaps does not understand the whole picture. You see, when argon naturally permeates to the outside, air is not exchanged to the inside of the IGU at the same rate. Each gas has its own idea of how fast it wants to move through a given polymer matrix. So, over the years, losing argon to naturally-occurring permeation can result in a negative pressure within the IG unit. This can lead to inflection, visible distortion and even IG unit failure as a result of stress build-up. Once again, be sure to review the argon permeability data in terms of identical measuring methods and units. If the measuring methods are the same but the results are listed in different units, the units can be converted, if necessary, to provide a meaningful comparison.
Weather resistance data is important not only in the context of the sealant itself, but more important in terms of how well a given sealant-spacer-glass combination stands up to the elements of weather exposure and cycling. The best data to look for here is performance of the IG units made with the exact combination of glass, spacer and sealant in an industry accepted weather cycling test. Currently, this is known as the HIGS test in North America. It can be conducted at one of the independent test labs participating in one of the industry test certification programs. A call to your sealant or spacer supplier should give you a big head start here, as they probably have these test results from existing customers or from their own testing.
Finally, you can choose the very best sealant for your IG fabrication, but if it does not process well on the equipment to be used, then application characteristics will suffer and so will workmanship. If you already own sealant application equipment, check with your equipment supplier to see what sealants are recommended for this particular type of machinery. Most sealant suppliers offer several grades of the same type of sealant and formulations are often offered which process better on specific equipment types. One key thing here is that flow rates must be high enough to provide fast application rates while maintaining adequate consistency so that the sealant stays in the cavity until it sets and doesn’t flow back out or “slump.”
Lately, I have noticed a trend toward either formal or informal manufacturing alliances among non-competing window fabricators. They are opening up the lines of communication and talking to each other more than ever about what works and what doesn’t. These types of relationships can be invaluable to help sort through the process of choosing the best spacer-sealant-process combination that is right for your business.
Jim Plavecsky is the owner of Windowtech Sales Inc., a sales and consulting firm specializing in the door and window industry based in Columbus, Ohio. He can be reached at
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