Architects Guide to Glass
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Fear Factor?
Adhesive Suppliers Guide Architects and Contract Glaziers in Designing and Installing Structural Glazing
by Ellen Rogers

Designing a structurally sound, aesthetically pleasing façade is the architect’s mission. Contract glaziers take on the task of installing the specified glazing system in a manner that ensures sound performance, while still maintaining eye-catching appeal. This is not always easy. Tie in the fact that architectural drawings are becoming increasingly complex and challenging—calling on the glazing systems to perform like never before—and it’s not hard to see why some may shy away from structural silicone glazing (SSG), particularly four-sided SSG (see related article on page 44 in April 2012 USGlass).

Fear not. Many sealant suppliers and manufacturers offer both contract glaziers and architects and abundance of resources, help and information that can guide them along the way.

Then and Now
When it comes to structural glazing, much has changed over the past few decades. Kevin Gerencser, vice president of in-plant glazing solutions for Tremco Inc., commercial sealants and waterproofing division, says since his company’s first structural glazing project in 1977, he has seen the industry mature and become more sophisticated as both knowledge and confidence have increased with using silicone sealants to adhere glass to buildings.

“This has resulted in a proliferation of structural glazed systems throughout the world,” says Gerencser.

In addition, the increased use of specialty coatings on the contact surface requiring primer, as well as more and more impact and bomb blast requirements, has also come to the forefront.

According to Doug Walker, vice president of sales and marketing of the facades, fenestration, insulating glass business unit for Sika Corp. North America, structural glazing has become one of the most popular methods of constructing unitized curtainwall.

“Once concerned, conservative suppliers of conventional storefront and curtainwall systems who were hesitant about offering anything glued in place now all offer standard two- and four-sided systems that are available to the general glazing community as opposed to those ‘bold and dangerous’ pioneering days,” says Walker.

Jon Kimberlain, application specialist, high performance building solutions, with Dow Corning, says one of the biggest changes he’s seen has been the move from site-glazing to unitized-shop glazing.

“Essentially, the glazing shop has become a factory where many curtainwall manufacturers now embrace programs such as Six Sigma and lean manufacturing to make the structural glazing process more productive and cost efficient,” says Kimberlain. “Two-part sealants that were introduced in the early 1980s appear to play a strong role in the transition as it has sped up the process of glazing by having a structural sealant that cures significantly in 24 hours versus one-part sealants that may take more than three or four weeks.”

Andy Shives, Americas marketing manager for Dow Corning, adds that when properly engineered, fabricated and bench-glazed SSG designs can help save energy costs to heat and cool buildings.

“The market has seen the proven performance is SSG, which has translated into more two- and four-sided SSG projects,” says Shives.

Product Evolution
Just as design trends change so, too, do products. Manufacturers are following changing architectural façades and developing, updating and improving their products.

“Other than the change in the early 1980s from an acetoxy-based silicone to neutral-cure products, and the introduction of a quick-cure, high-modulus one-part, neutral-cure silicone for on-site four-sided structural work, bomb-blast and impact-glazing systems, minor changes have been made to existing products,” says Gerencser. “These [changes] improved handling characteristics making them easier to use without compromising their proven performance characteristics.”

He adds one major change, though, was the introduction of a gasket weatherseal on unitized systems.

“This virtually eliminated the need to ‘swing stage’ the building once the curtainwall was installed,” he says.

Walker says his company has also modified and updated products. He says they have developed new products to meet the changing trends of new metal finishes such as high PVDF-content paints and fast-curing one-part and two-part cartridge systems for replacement and field installation work.

Shives adds that his company has also continued to update and improve products.

“We have SSG products for impact resistance and protective glazing,” he says, explaining that there are products available today that provide more design freedom with increased movement capability compared to some of the earlier developments.

Questions Answered
While SSG systems have become commonly designed and installed over the past few decades, both contract glaziers and architects alike still have concerns. For example, Gerencser, says these often relate to performance matters, such as the history of the product’s usage in the field; compliance to ASTM specifications; adhesion and compatibility testing; inspection and follow up procedures; quality control on site and in the plant; and warranties.

“Once the performance issues are addressed architects will focus on the aesthetics of the products, such as color, while contractors concern themselves with the delivery system (pump programs) and ease of applications, snap time and in-plant follow ups by the manufacturer to ensure consistent quality,” says Gerencser.

Kimberlain adds that these questions can run the full spectrum, depending on how comfortable each party is with structural glazing.

“We still have architects who are doubtful in the durability of structural glazing even with the practice approaching 50 years,” he says. “Most discussions today revolve around sustainability and how structural glazing plays a role over other choices of glazing by providing a perimeter seal between the glass and frame to help reduce or eliminate air infiltration ...”

According to Walker, most questions relate to the support they will receive in terms of testing, recommendations and warranties.

“As structural glazing continues to grow and designs evolve to incorporate the use of more glass in unique ways, the need for this support has become even more critical,” says Walker. “A concern has been compatibility between products and the coordination of trades installing them.”

Lean on Me
As a way to support contract glaziers and architects, many sealant suppliers offer a variety of resources and support services.

These include AIA-accredited courses for architects, web-based learning systems, tech-service support, drawing review and assistance, adhesion and compatibility testing both before the job and during fabrication, as well as application and testing protocols for both the site and the plant.

“For architects, engineers and consultants we offer ongoing continuing education programs as well as individualized design and specification support,” says Walker. “For glaziers we offer product training, laboratory and field testing and on site assistance as needed.”

According to Kimberlain, his company offers several different educational avenues.

“One is the publication of our Americas Technical Manual, which outlines the recommended practices for successfully glazing with silicone sealants and a key component in achieving warrantable projects desired by the glazier, architect and building owner,” he says. “We have been using webinars to deliver training to our channel partners to ensure proper use and support of our product. And we are always happy to provide individualized education seminars to anyone interested in understanding the how’s and why’s of structural glazing.”

And manufacturers all agree that testing is essential.

“It is critical with structural glazing systems as you are adhering glass to the building with a silicone bead,” explains Gerencser.

“Compatibility testing is undertaken at the onset of the job to ensure the long-term performance of the system is not compromised by products in contact with each other, negatively affecting each other over time.”

Gerencser also notes that a separate set of tests are required for plural-component silicones to ensure consistency in mix and product and system performance.

“We conduct plant start-ups including initiating log books and testing protocols and procedures, which include butterfly tests to ensure uniform mixing, snap times to confirm cure consistency and, most importantly, adhesion tests to verify continued performance of the system. The results are logged daily or as required,” he says.

Walker agrees this is important, as the substrates to which structural adhesives must adhere or with which they come in contact can change from project to project and between suppliers.

“Each project should always be tested with the production materials to be used on the project, not representative or color-approval samples, such as in the case of paints for metals,” says Walker. “It is also a useful mechanism to ensure the structural sealant supplier and installer are talking, reviewing the project together and are in concert with how the job must proceed.” He notes that for many suppliers there is no charge for this service.

"Once concerned, conservative suppliers of conventional storefront and curtainwall systems who were hesitant about offering anything glued in place now all offer standard two- and four-sided systems that are available to the general glazing community as opposed to those ‘bold and dangerous’ pioneering days."

—Doug Walker

“Product testing is very important to confirm all the materials coming in contact with the silicone are compatible with each other and will perform as expected,” agrees Shives. “There is variability in many substrates so it is important to test for every single project. This is also required in order to receive a warranty.”

Walker adds, “It’s important for anyone involved with structural glazing to remember the structural sealant is the most important, strongest link, which quickly becomes the weakest if not done correctly.”

And, as Kimberlain points out, “It’s a means of validation that the material will perform as intended, it was designed on paper. Structural sealant manufacturers offer a 20-year warranty, but the reality is that buildings are expected to perform much longer so we are really looking at forever-types of designs. Without the testing, the design only performs on paper until it is built.”

Forward Thinking
Looking ahead, adhesives experts expect to see continual evolution in terms of both design and construction.

“We will see a continuing, increased use of unitized or in-plant wall systems. This is due to better quality control but, more importantly, it [helps] reduce construction cycle time, reportedly up to three months,” says Gerencser. Other changes he expects to see include the development of sealants that build cure and tensile quicker without compromising adhesion, which can also further reduce cycle times.

Walker adds that, from a design standpoint, he expects to see not only the increased use of high-performance glass, but also the use of other materials—such as concrete, stone and metal combined with glass incorporated in the facade

“We also foresee more companies incorporating more of the envelope into their scope of work, more single-source responsibility and [adhesives suppliers] providing more than just products but product lines consolidated into systems and methods to achieve the goals that meet or lead the trends.”

Many of the expected future changes also relate to energy-efficiency and glazing, such as the increasing use of high-performance films in insulating glass units (IGU), triple-glazed units and electrochromic IGUs.

For example, Gerencser expects to see more dual-wall systems, which can help improve energy efficiency, while increasing the amount of natural light that enters a structure.

“Buildings will be commissioned to deliver an energy-efficient environment where the envelope and internal systems of the structure are balanced to achieve a sustainable environment,” he says.

Walker adds that the industry will likely need “to coordinate with other trades to make the proper connections, transitions as well as adopt new technologies and trades skills, such as those required for solar or electrochromic glazing applications.”

Also in the future, expect to see projects that push the design strengths of the silicone bite in an effort to reduce the amount of metal in mullions.

“Energy and sustainability will be the driver as metal provides high heat transfer and can impact energy loads,” says Kimberlain. “Decreasing the metal also will impact the overall bottom line of the total building cost, as it is a large portion of the building façade.”

But the challenge, he points out, will be how to properly develop the methods of engineering analysis and testing validation to prove higher loads are appropriate for designs.

“As I said, we are really looking at the forever business,” he says. “Changing design stress on a proven technology that has worked for more than 40 years should not be changed with the stroke of a pen.”

Looking at the growth structural glazing has seen these past 30 or 40 years, Gerencser adds, “Structural silicone glazing has had a long history of outstanding performance based on rigid (but simple) procedures and guidelines to follow, which should be maintained to ensure continued success.”

Ellen Rogers is the editor of the Architects’ Guide to Glass & Metal magazine, a USGlass magazine sister publication. She can be reached at erogers@glass.com or follow her on Twitter @AGGmagazine and like AGG magazine on Facebook to receive updates.

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