Volume 48, Issue 7- July 2013
Silicone is Silicone...Actually, it’s Not
Just because a particular brand of silicone sealant worked great on one project, doesn't necessarily mean it will fit the bill on the next. A number of challenges and issues can arise if sealants are specified and ultimately installed improperly. As such, the glass industry has before it a tremendous opportunity to educate architects and specifiers about what they need to know when it comes to proper sealant uses for their varying designs.
Knowing the Difference
There are differences in sealant types. Organic sealants consist of a carbon-based polymer and inorganic products are non-carbon based.
"Silicone is an example inorganic sealant made from a silicone polymer backbone," explains Mary Altenburg, construction account specialist with Dow Corning based in Midland, Mich.,. "[With] silicone, ultra-violet (UV) light will not degrade the silicon-oxygen polymer bond," she says. "UV will degrade the carbon-oxygen bond of organic sealants, but not silicone." She says that while the silicone is more expensive, it has a longer life-span than organic products providing life-cycle savings.
According to Glenn Heitmann, president and CEO of St. Louis-based Heitmann & Associates, a curtainwall consultant, while inorganic sealants are commonly used for structural applications, organic sealants, on the other hand, are typically used in green, residential work for wood and some concrete applications. Silicone sealants are the only products recommended for building structural glazing applications, Altenburg explains, as organic sealants do not provide the same level of strength and durability as silicone.
“So many times there is the thought that a sealant is a sealant. But there are different types,” says Heitmann. “Understand what you need your sealant or caulk to do for you, and then specify the right product for the right application for the right performance.”
He adds, “Architects are generally under the impression that sealants are the same and they are not, even those within their own product family.”
"Some people think silicone is silicone, but not all are created equal," agrees Altenburg. As an example, she explains some have structural integrity, while others do not. "Some bond well to concrete without a primer, while others require a primer to do so. Some silicones have 25 percent movement capabilities and some have 100 percent; the wrong silicone could also cause corrosion on some metals.”
Altenburg points out architects should also be aware that a siliconized acrylic sealant is not the same as a silicone sealant. "That just means a silane or silicone ingredient has been added to improve acrylic; it does not have the same properties. Structural silicone is long lasting and it's important to know that UV does not degrade it or cause it to breakdown. Durability is the key word."
According to Bill Davis, technical sales engineer with Sika Corp. in Madison Heights, Mich., some key considerations involve the specific design details, project organization and achieving proper adhesion to the substrate. He says the questions that most commonly arise involve compatibility, adding that it’s not unusual, for example, to have one sealant supplier for the insulating glass and then another for the structural portion as well as with accessory materials.
“Often a common misconception is that when there is a failure it’s because something was [wrong with] the sealant. It may not be the sealant, but rather something in terms of incompatibility,” says Davis “It could be an IG failure, for example, so it’s important to manage components and monitor projects closely.”
What Do I Use Here?
There are also considerations when it comes to the application itself and the type of adhesive to use.
"First you need to understand the basics of choosing the right sealant. You need to know what the surfaces are to which the sealant must adhere," says Altenburg. "That's an indicator; the substrate must be identified, as well as the design of the building. If you use the wrong type of sealant it could crack, become gummy, harden, etc., so you want something that's long lasting and with good adhesion.
According to Paul Becks, executive vice president of National Enclosure
Co. LLC in Ypsilanti, Mich., there are a number of areas with which architects
should be familiar when it comes to designing a structural glazing project?
Becks suggests architects know the answers to these questions:
Becks, says architects also need to understand the materials that can be relied upon for proper adhesion.
“Not all painted surfaces will work for proper adhesion. The other major issue is to understand the quality control processes that are required to assure properly cured and performing structural sealants.” Becks explains that the manufacturer of the sealant will dictate a specific regimen of testing the sealant compound for two-part mixes (the butterfly test) and samples to be used for pull testing.
“It is also important to maintain records of what material and lot numbers are used where, and to document atmospheric conditions at the time of installation,” he says. “It is important to assure that the installer is properly trained in the application process and what constitutes a properly installed joint.”
He continues, “Improperly prepared surfaces will result in loss of adhesion and structural failure. Oversized joints (too thick) will not allow proper curing and may result in joint failure. Field-applied joints installed in poor atmospheric conditions (too cold /too dry) may not cure properly, resulting in failure, and improperly secured temporary blocking allowing movement will result in joints failing prior to reaching full cure.”
Heitmann says that there are a number of other details in addition to the material and application that must be considered. “What’s the size of the joint where you’re using it? Are you using it with backerrod? Those go beyond just what adheres to [the substrate] be it glass, etc.,” he says, noting that one of the most common problems is a lack of adhesion.
“And that could be a structural aspect, and it certainly could be a weatherability issue. If it’s used as the primary [seal] to hold back external elements then you might have shrinkage and possible reversion over time.”
Heitmann says while materials are often selected for their aesthetics, it’s equally as important to know the byproducts, particularly with sealants.
“[It] could be the weak link because it impacts everything,” he says, explaining there can be concerns of leaching, contamination and discoloration.
Keeping Up With the Changes
Adhesives and sealants for glazing applications have undergone exponential changes over the past 30 years. As a result, building designs and aesthetics have become more complex. With an increasing reduction in the amount of metal being used, sealants are being called on to play a significant part in the design, often leaving architects with many questions.
"'What sealant should I use,' is a pretty common question," says Altenburg. "Architects also ask for recommendations when it comes to structural glazing."
She says they want to know what sealants meet certain specifications or test requirements. (see box to left).
Davis agrees that, with these product evolutions, sealants are being called on to do more and more. For example, he says products are available that will allow architects to design with a smaller sealant bite than in a typical installation, resulting in the use of slimmer aluminum mullions.
“It results in more vision area, materials savings and less metal so there is a less thermally conductive façade, which can help in earning LEED credits,” says Davis, adding that such new developments give architects a “higher level of design freedom.”
Contract glaziers also have an important role to play. The glaziers, for example, can define what materials should be used for the project and can do so on the front end.
“The glazier can say ‘this is what is specified, but here is what should be used and here’s why,’” says Heitmann. “If you know it’s a problem, why put it up? Whether the project is design build, design assist, etc., contract glaziers can give a reasonable design intent of what’s important and then come up with the system to ultimately meet that performance.”
No matter how glassy, how transparent the architect envisions the facade, the most important design consideration is that the building be safe and structurally sound.
"You want to make sure and understand the movement limitations are for sealing building joints," points out Altenburg. “During the design phase it's important to have an understanding of what the structural silicone can and cannot withstand."
Davis adds, “They should not ignore the developments in sealants and adhesives when designing facades. It’s an opportunity for them … to have aesthetics, energy efficiency and material savings on façade designs.”
Sharing knowledge and information among those involved in the design process is also an important step in ensuring a successful project. Davis says suppliers can work to educate architects, working with them to offer seminars and continuing education courses.
“This is particularly important to younger architects who are still learning the business,” he adds.
And to help architects avoid the potential for such problems, Becks agrees the best help he can offer is simple.
“A short education on the pitfalls and limitations, followed by instruction on proper techniques,” he suggests. “You may also introduce the sealant manufacturer’s technical representative for follow up questions.”