How Silicone Enhances Glass Durability
By Joshua Huff
Glass can only do so much to ward off the elements. Fortunately, it doesn’t have to do so alone. Along with a variety of high-performance components, parts and sealants, these systems help ensure a building’s interior remains safe and snug. Silicone, for one, is commonly used on construction products worldwide due to its durability and versatility, making it a popular choice for glass applications and door and window installation.
Brian White, technical section manager at Minnesota‑based H.B. Fuller, says silicone offers excellent temperature and weather resistance, ultraviolet (UV) stability and flexibility. It is also used for its aesthetic appeal, providing a clean and seamless look, while in some cases eliminating the need for fasteners or clamps.
“Silicone is found in several important applications when used in a structurally‑glazed façade,” explains White. “It serves as the secondary sealant in the insulating glass unit (IGU) edge seal, the weather sealant found at the joints between IGUs, and the replacement for mechanical fasteners securing the IGU to the structural components of the façade.”
Doug Walker is the national structural glazing commercial manager at Momentive Performance Materials in New Jersey. He says silicone’s UV stability is unmatched, making it the most used product for glazing. Of course, the quality of the silicone determines its effectiveness, ensuring the longevity and performance of IGUs, which is why many steps go into the process of deciding which silicone to use.
Types of Silicone
Walker explains that many types of silicones are used throughout the construction industry. These include penetrating sealers, transitional sealants, gaskets and setting blocks, air and vapor barrier coatings, precured silicone extrusions, waterproofing restoration coatings, weather sealants, IGU secondary sealants and structural silicone glazing (SSG) sealants.
“The most widely used of these are IGU and SSG sealants,” notes Walker.
White adds silicone is available in one‑ and two‑component formulations that vary in ease of application and rate of cure. The most commonly used are two‑component, neutral‑curing silicones, which White says generally offer the fastest handling time and are compatible with other components.
Vicente Montes, vice president and façade engineer at Dallas‑based Curtainwall Design Consulting, says not all silicones are created equal. Numerous sealant brands exist worldwide, and each region favors a particular brand. Choices vary from market to market.
Choosing the Right Silicone
The selection of products begins early in the design phase. Walker says engineers are responsible for choosing the proper products and determining the adhesive bite size and geometry in cases of bonding silicone.
Additionally, silicone manufacturers conduct adhesion, compatibility and print reviews to confirm selection and offer further advice when needed. Walker says that, ultimately, adhesive performance is the most important decision, especially for IGUs and SSGs.
Walker says the decision process typically begins with product selection via a datasheet, consultation with the distributor or manufacturer, lab testing when required, and site testing of conditions and application quality. He adds that cure times are standard per product and joint size, but they are confirmed by unit deglazing for SSG.
“Different glass types don’t need to use different silicone types other than the correct ones for either IG, SSG or weather seals,” says Walker. “What may vary is the surface prep method used. Silicone bonds perfectly due to its chemical similarities to glass; what will vary is any coating, intended fall application and whether it’s shop‑or‑site applied.”
Montes says CDC looks at the whole picture when it receives a project. Glaziers will use one type of silicone, while air barrier contractors typically use a different sealant.
“When a glazing system abuts an air barrier system, we need to check what the air barrier contractor will use and what the glazier will use,” says Montes. “When they do their submissions, they typically don’t talk. Sophisticated general contractors pay attention to this, but sometimes they don’t. That’s where we justify our presence as consultants. We have to look at the different products used to ensure there are no compatibility issues.”
H.B. Fuller’s senior research and development manager (engineer adhesives), Harald Becker, says various ASTM guides and specifications help select the correct silicone for the desired application.
For example, ASTM C1249 and ASTM C1369 are particularly important for IGU secondary sealants. Weather sealants generally conform to ASTM C920, while ASTM C1184 and C1401 will help a fabricator decide on what product to use as the structural glazing silicone.
Becker explains that different substrates (e.g., types of glass and framing materials) could require specific testing to ensure the silicone candidate performs to applicable ASTM standards. Adhesion to all types of glass, glass coatings and coated steel or aluminum must be tested before use.
Montes agrees that testing is vital.
“It’s important to do field‑and‑material testing before the project just to make sure that the sealant chosen is the correct one and to determine whether you need a primer so the sealant sticks,” he says.
Does Silicone Impact Interlayers?
Not often, says Vaughn Schauss. He is the Americas Technical Consultancy manager for Houston‑based Kuraray America Inc.’s Advanced Interlayer Solutions Division. He explains that blemishes, discoloration and tiny bubbles can form when silicone comes in contact with the edge of laminated glass; however, alterations will not impact the laminate.
He says the worst that can happen is that the silicone fails over time and allows moisture in, but that’s a maintenance issue, not an installation or product problem.
Schauss says to mitigate issues, communication and testing, such as accelerated weather testing, are key. That’s because there are numerous sealants and interlayers on the market. The only way to test their usability is through trials, such can last up to 21 weeks.
“When it comes to accelerated weathering testing, you simply put the components together, place them under high heat and humidity, let them sit there for a long period of time and see what happens,” he says. “That’s how the industry judges whether they are compatible.”
Schauss says that as long as the laminate is made properly and the sealant is in good shape, they do well together.
Common Failures
Walker says that while defective silicone products are rare, failures do occur. They are usually caused by poorly designed systems, bad installations, improper selection, lack of testing or consultation before testing, inadequate surface prep or general application error.
“It’s like with most products,” says Walker. “You have to assume the right one is selected, stored properly and used in shelf life.” White adds that proper primer and cleaner use and mandatory factory production control procedures should be in place on the glazing shop floor and in the field to avoid application failures.
Common Causes of Bond Failures
Brian White, H.B. Fuller’s technical section manager, says that common causes of bond failure include chemical incompatibility between different silicones and other components, along with:
• Poor quality control when mixing two‑component materials;
• A lack of appropriate cure time before handling;
• Contaminated substrates;
• Improper surface preparation (i.e., lack of recommended primers); and
• A lack of communication between all component suppliers so that all parties involved in the fabrication of the façade understand the performance requirements.
Joshua Huff is a contributing editor for [DWM] magazine.
jhuff@glass.com
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