Experts Clear Up Misconceptions About Laminated Glass

By Jordan Scott

Laminated glass gives architects and designers the ability to improve safety and sound attenuation. It can also provide strength and the means for artistic expression. With a number of possible functions of laminated glass beyond just transparency and daylighting comes many misconceptions. Lamination experts are shedding light on the truth behind these misconceptions.

Misconception: Fully Tempered Glass is the Only Safety Glass

Julia Schimmelpenningh, industry technical manager for architectural products at Eastman Chemical Co., says one misconception is that tempered glass is the only safety glass.

“Many times, in marketing and informational brochures from some associations and organizations you will see reference to safety glass (fully tempered) or tempered safety glass as the only material that complies with codes,” she explains.

In the correct configuration laminated glass also is safety glass and does not need to incorporate tempered glass to be deemed as such, according to Schimmelpenningh. The material simply needs to meet the requirements of CPSC 16 CFR 1201 or ANSI Z97.1.

“The building codes reference the performance and not the type of safety glazing except when glass fall-out is a concern. In these cases, they specifically reference laminated safety glazing (skylights, overhead, balcony, etc.),” she says.

Misconception: Hurricane Glass Is Bullet Resistant

Ron Hull, Americas marketing manager for Kuraray America’s PVB division, says he’s had to correct people on the differences between hurricane-rated and bullet-resistant glass.

“This discussion is usually around school security and schools starting to harden buildings,” says Hull.

Schools from Texas to Maine have hurricane-rated glass and as people worry about keeping schools safe from attacks, some think that glass can do the job.

“To be bullet-resistant the glass has to be much thicker, like closer to 1-inch thick, to stop the smallest of bullets,” explains Hull. “People working on schools sometimes even want the whole building to have bullet-resistant glass, which is too expensive.”

Robert Carlson, who works in mechanical engineering at fabricator Tristar Glass in Tulsa, Okla., adds that glass doesn’t need to be bullet-resistant to provide some forced-entry resistance, which can prevent a potential attacker from entering a building until first responders arrive.

Another misconception is that the specification can just include the hurricane glass, rather than an entire system.

“People ask if they can put in hurricane-rated glass, but the whole system has to pass the hurricane rating together, not just the glass,” explains Hull.

Misconception: An IGU’s Outboard Lite Should Be Laminated

Carlson says he sees laminated glass specified as the outboard lite in hybrid insulating glass units (IGU), but there are few situations where that’s needed. Using an IGU with laminated glass provides protection and insulation for energy efficiency.

“In a chemical factory where you’re worried about an explosion from the inside hurting people on the street it makes sense, but the laminated lite should be placed toward the area you’re trying to keep safe,” he explains. “If there’s wind or an explosion on the outside of the building then it will keep the people on the inside of the building safer if the laminated glass is the inboard lite.”

Carlson also says that putting the laminated glass as the outboard lite increases the cost of a unit and the challenge of fabricating the unit.

Misconception: Exposed Edges on Laminated Glass Can’t Look Nice

Hull says that many specifiers think exposed edges on laminated glass won’t look neat. While the edges of laminated glass likely won’t look as good as the edge of a monolithic lite, Hull says Kuraray works with many fabricators who can make laminated glass with an attractive edge for frameless applications.

Carlson adds that, depending upon the quality of the fabrication, delamination may only happen on a 1/16- to ¼-inch of the glass around the edge.

“The safety that product provides and the long-term look and durability benefits greatly outweigh any delamination that could occur over time … If a handrail broke a kid won’t fall and that’s more important than the fact that it’s slightly delaminated,” he says.

Misconception: Laminated Glass is Not Suited for Exterior Applications

Schimmelpenningh says that laminated glass with PVB interlayers are well suited for exposed and external applications, despite the misconception.

“All materials should avoid standing water or chemicals at the edges. The products have changed over time and specialty products with ever-evolving durability and capability have been and continue to be introduced into the marketplace,” she says. “These interlayers are not the same ones that were used decades ago.”

Earlier PVB interlayers were more susceptible to visible delamination due to high moisture, stress or mismatch than the PVB interlayers that have been made since the late 1990s, according to Schimmelpenningh. However, when laminated glass delamination is seen in an exterior environment it is easy to make the assumption that all products are not capable of that particular use.

Misconception: Increasing an Interlayer’s Thickness Improves Acoustic Testing

While increasing the thickness of an interlayer may provide a slight change in sound attenuation, Hull explains that simply changing from monolithic or insulating glass to a PVB interlayer will provide the most significant change.

Carlson says switching from a regular interlayer to a sound control interlayer can make a big difference, but many people think adding more interlayers will improve sound attenuation.

“If you compared one sound control interlayer to four layers of a regular interlayer, the difference in sound reduction is kind of negligible,” he says.

Misconception: A .030-Inch Interlayer Will Work with Heat-Treated Glass

Carlson says he also commonly sees specifications calling for a .030-inch interlayer for heat-treated laminated glass.

“Due to the nature of heat treating, roller waves and distortion, you typically want to use a .060-inch thickness interlayer … It will fill any discrepancies between the profile of the two lites,” he explains. “People say they want .030 to reduce costs or they just pick an interlayer.”

Misconception: PVB is PVB

Hull sometimes looks at specifications and sees only laminated glass listed.

“There are a lot of different applications where you may need different types of laminated glass. One way to clear this misconception up is to let specifiers know that there are more than just PVB interlayers out there. There are other interlayers such as ethylene vinyl acetate (EVA) or ionoplast,” says Hull. “The specification might just list safety tempered or laminated glass but, for example, in glass for structural projects the specifier should be
specifying a structural interlayer and not just laminated glass.”

The same would apply for acoustic applications. Hull recommends specifiers specify an acoustic PVB instead of just PVB. He says it’s important to help specifiers understand the many options available in laminated glass.

Schimmelpenningh says that prior to the late 1990s, one type of PVB interlayer which consisted of a basic formulation of resin and plasticizer was dominant.

“Therefore, this type of PVB was monikered with a generic name which most still use today,” she explains. “There are several types of PVB interlayers available. Most are highly engineered adhesives that are targeted to provide the basic safety glazing performance, but are also modified to provide other value-added and desirable characteristics. Today’s various PVB interlayers can deliver safety and security, impact resistance, noise mitigation, solar control and UV screening as well as structural performance and color options. They are designed so that the various formulations from the same supplier can also be combined to help meet the project needs – for instance an acoustic interlayer can
be combined with color to provide security and wayfinding to a school.”

Misconception: EVA is Not a Strong Product

“There’s a general misconception that if glass is laminated with EVA it can’t receive approval for things such as safety glass, but that’s not the case,” says Pete deGorter, vice president of DeGorter Inc., which represents machinery manufacturer Pujol.

He adds that it’s the best option when used in an open cap rail system where it’s supported by only one side.

“It won’t allow the glass to fall if both lites break, but it’s not as rigid as ionoplast,” says deGorter.

He attributes many of the misconceptions around EVA to Young’s modulus, a mechanical property that measures the stiffness of a material. He says this modulus looks at the interlayer only and those that are PVB and ionoplast perform better in terms of stiffness. He says EVA is very strong when measured using the shear modulus, which takes the interlayer’s bond to the glass into account.

EVA was designed for solar applications in space, says deGorter, meaning it has a larger thermal gradient of temperatures where it remains stable. deGorter says EVA’s thermal gradient is larger than that of PVB which can become brittle in extremely cold temperatures and soft at extremely high temperatures. This makes EVA a suitable option for extremely cold or hot climates where it is less likely to fail in cases where PVB or ionoplast might, according to deGorter, who says it’s also less likely to delaminate.

Misconception: PVB is Only for Automotive Applications

One of the early and biggest markets for laminated glass was for car windshields. PVB interlayers have been used in the automotive market for approximately 80 years, but Schimmelpenningh says they’ve also been used successfully in the architectural market for nearly 60 years.

“The products have evolved to meet the needs of the markets they serve and are no longer a one-size-fits-all product. They’ve been specially engineered to provide the characteristics demanded of them by the markets they serve. In the architectural market, that means having the ability to act as a safety glazing, retaining glass shards for some time
when broken and wet, and providing a mechanism to keep a building envelope intact, its occupants safe and comfortable, and the properties protected,” she says.

A Look at Different Interlayer Types

Laminated glass comes in a wide variety of shapes and sizes, offering many different performance capabilities and aesthetic benefits. There are several different types of interlayers that could be used in laminated glass configurations.

Polyvinyl butryl (PVB): PVB has a clear finish and is a low-cost interlayer option, making it the most common. It’s also offered in a variety of colors and thicknesses. To correctly process PVB, it must be climate controlled for both temperature and humidity.

Ethylene Vinyl Acetate (EVA): EVA is suitable for laminating metal, wood and other non-glass materials to glass. It’s also used under very wet conditions such as a swimming pool or sauna. EVA is not as clear as PVB and can be more expensive. Capital requirements for producing EVA are much lower, though, as it doesn’t require special climate control for processing.

Glass-Clad Polycarbonate: This glazing make-up is constructed of layers of glass, urethane and polycarbonate, and the laminating process is the same as with PVB. It can be used for applications that require safety and security, such as blast- and bullet-resistance and forced entry. A glass-clad polycarbonate provides high levels of resistance without spall.

Structural Interlayers: This type of material is much stiffer compared to traditional PVB and is commonly used in applications such as overhead glazing, glass balustrades and those with minimal support.

Poured Resin: The poured resin process begins with two lites of glass separated by an edge tape. They are then placed together on a horizontal vacuum table. The resin is pumped through a nozzle into the cavity formed by the edge tape on a tilting table, which tilts the glass until the resin has filled the space between the lites uniformly. The glass unit on the table is then moved underneath ultraviolet lights which cure the resin. Once cured, the glass edges are cleaned.

Protective Glazing Product Highlights

PRL: Bullet-Resistant Glass

PRL’s security glazing products provides security, no-spall ballistic protection and scratch resistance. The company says its laminated standard glass level 3 is 1.10 inches overall thicknesses, which is thinner and lighter compared to other products on the market. Guarding against a collection of weaponry and ammunition, the safety glass can be used in a number of interior and exterior applications. Fabricated in-house, PRL’s bullet resistant
glass is made up of the company’s proprietary blend of glass, PVB and
polycarbonate.

www.prlglass.com

Salem Flat Glass & Mirror: Hoaf Heatbox

The Hoaf Heatbox available through Salem Flat Glass & Mirror, has nearly all safety glass lamination needs covered. Using infrared technology in autoclave-free lamination, the Hoaf Heatbox was developed to cost-effectively laminate safety glass with PVB, EVA and TPU, according to the company. As with all Hoaf machinery, this component is a self-contained modular unit designed for “plug and play” installation. The Heatbox can
laminate glass of all thicknesses and shapes and can be used for the heat soak test.

www.salemdist.com

Trosifol® World of Interlayers: Forced-Entry Resistance

Trosifol World of Interlayers has completed testing on forced-entry resistance. Glass constructions with Trosifol PVB and SentryGlas® ionoplast interlayers can provide protection against physical attack from 50 seconds to over 13 minutes, according to the company. For bullet-resistant glazing, the products have passed UL752 and NIJ 0108.01 testing protocols. The company’s portfolio of products ranges from those that are soft for acoustic applications to those that are stiff for structural and security projects.

www.trosifol.com

Vitro Architectural Glass: Heavy Starphire Ultra-Clear® Glass

Starphire Ultra-Clear glass by Vitro Architectural Glass helps give heavy glass projects what the company describes as a jewel-like clarity. The glass can be used in a variety of applications, including those for safety and security, and is available in thicknesses up to ¾-inch (19 mm).

For special projects, such as zoo enclosures, display cases and protective windows, Starphire glass provides 16 percent higher visible light transmittance than ordinary clear glass in a 1 3/8-inch laminated construction, according to the company.

www.vitroglazings.com

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