Creating Aesthetically Pleasing Exposed Edges With Laminated Glass

By Jordan Scott

When it comes to achieving good quality edge work, fabricators often are caught between the aesthetic demands of architects and ASTM standard guidelines. This has become more of an issue in recent years since the 2015 International Building Code required that fully tempered laminated or heat-strengthened laminated glass be used in railings with a 30-inch drop.

An interlayer sandwiched by two glass lites must be used in such applications to prevent the small pieces of shattered tempered glass from falling on someone walking below the glass. Keeping the glass in the opening also can prevent someone behind the railing from falling.

Aligning the edges in laminated glass is not always easy, and it’s a topic of conversation among fabricators as architects continue to desire minimal hardware in railings and other glass applications to maintain transparency and views.

Edges Exposed

Jim Smith, director of Invisiwall engineered glass systems at Consolidated Glass Holdings (CGH) based in Pedricktown, N.J., says that his company is seeing more applications with exposed edges, including handrails and canopies.

“Edge conditions on laminated glass are critical to getting the aesthetics [architects] want … We’re seeing a lot of architects pushing the envelope for superior edge conditions that only a few fabricators can adhere to,” he says.

Brian Dawley, senior technical services representative for Viracon in Owatonna, Minn., says his company tries to hold tolerances tight so the glass doesn’t slip too much during the lamination process. He explains that his company keeps tolerances tighter than the ASTM C1048 standard requires.

“Edges can still be within tolerance and visually appear slightly off,” he says, adding that if the edges are within tolerance they are considered good. “If deemed unacceptable they would purchase a new lite and hopefully get quality more to their liking.”

Achieving Alignment

Paul Mouton, senior sales development at Midwest Glass Fabricators (MWGF) in Highland Township, Mich., says that while fabricators can achieve tight tolerances, it’s important to educate architects and glaziers on what’s reasonable.

“If an architect wants to hold the tolerance to 1/64th of an inch, much like monolithic glass, that type of tolerance is not achievable unless using high precision equipment which is expensive,” he explains. “A lot of times they’re putting that in the spec because it was something handed to them in their drawings. It’s not terribly reasonable.”

Smith explains that while CGH’s techniques are proprietary, great detail goes into the preparation of the product before it goes through temperature changes in the autoclave to promote polymer flow.

He also points out that if there are discrepancies in the size of the two lites of glass used, it will cause misalignment no matter what a fabricator does.

“The pre-oven process needs to create good alignment and stability before the product is put into the oven,” says Smith. “… There also needs to be special attention paid to trimming and post production. This is often done by hand.”

Ultimately, the best practices involved in achieving aligned laminated edges depend upon the lamination process used and the type of interlayer. There is no prescriptive method across the board.

MWGF uses two different lamination processes: a bladder laminator and an autoclave. The bladder system uses a vacuum to seal the glass so there’s no movement. It uses pressure plus heat to laminate the glass in a horizontal position. In the autoclave process, the two glass lites and interlayer are first put through a tack oven to get the unit to a temperature just warm enough for the interlayer to tack to the glass. It’s then put into an autoclave where pressure forces the interlayer into all of the pores of the glass,
ensuring that the unit doesn’t delaminate.

MWGF uses the bladder system for SentryGlas Plus (SGP), which Mouton says is more successful versus the autoclave. MWGF also uses the system for multi-layer applications such as bullet-resistant glass.

“We will use that horizontal bladder system for bagging and it keeps the index almost spot on,” he says, adding that he recommends avoiding trying to bag large units and then moving them to a vertical application such as an autoclave. “We learned very early on that oversized pieces in a bag, even when we use the best of care, as we stand them up there’s the chance for it to shift in the bag since the interlayer is not tacked to the glass … If bagging, ensure that the edges, whether clamped or something else, are well aligned before putting it into a horizontal or vertical autoclave.”

Mouton also recommends sending all units through the lamination process as matched pairs from the same batch.

“Use matched pairs from start to finish. If you can get both lites of glass from one large piece of glass that’s helpful,” he says.

Mouton explains that one worker could cut the glass 1/16th of an inch shy while another cuts it spot on but if one cuts shy and the other heavy, then the tolerance could be a 1/8th inch off, which is a more noticeable difference.

“The more you can match the pairs from the same cut the better chance you have of laying it out and making sure your laminated unit is close to perfect as it runs through polishing and tempering together. If you’re fabricating holes, the holes should be fabricated at the same time so you have multiple opportunities to [ensure] quality control before you get to the most extensive process, which is laminating,” says Mouton. “To make the edge as pretty as possible we put a little overage on the laminate so we know we
can fill the arris to give it a straight, clean aesthetic.”

He adds that, if the glass shifts in the lamination process, it might be possible to see the difference in how the glass lites are indexed together. With annealed glass MWGF can run the laminated unit through a pass in the polisher after the lamination process.

“We can take the glass from the autoclave and run it through the polisher for a nice aesthetic. It’s cleaner than the multiple arrises created from tempering,” says Mouton.

No matter which laminating method a company ultimately decides to use, Mouton says it’s important to make sure it’s appropriate for their market, abilities and level of investment.

“Know your market and know where investment levels should be to get the appropriate equipment to do what you need to do. Give yourself room to maneuver to be able to work on the glass itself. You have to have a lot of space for trimming and inspecting. It’s a little bit different than inspecting on the back of a tempering line. You have to put it on a table, look for air bubbles, stand the glass up and make sure your distortions are going in the same direction to make sure you’re creating a high quality piece of glass,” says Mouton.

To Post-Temper Fabricate or Not

Is the post-temper fabrication of glass a safe and acceptable practice? This topic comes up especially when looking at how to achieve aesthetically pleasing exposed edges with laminated glass.

Bill Lingnell of Lingnell Consulting hopes there will be industry participation by temperers to quantify how much post-tempering fabrication weakens the glass.

“This would help engineers and architects to know what the limits are,” he adds.

Pulp Studio CEO Bernard Lax says his Gardena, Calif.-based company has post-polished tempered and laminated glass to achieve smooth edges since 1998. Pulp Studio offers a warranty on its edge work, which Lax says is necessary since there is no ASTM standard
for fabricators to point to in the case of post-tempering fabrication.

“It is the manufacturer’s job to warranty the glass as processed and accept and take on the liability,” he says. “… It’s impossible to mandate an ASTM standard and there will always be hurdles to a final acceptance of this process. In the end it is about the glass performance and the warranty is what creates the comfort zone for acceptance in a project.”

Lingnell described a warranty on post-tempering fabrication as an individual business decision.

“If somebody wants to warranty it and stand behind it they can, but right now the standard ASTM C1048 as it exists suggests no post-fabrication to tempered glass,” says Lingnell. “The standard’s aim is to protect the glass so people don’t take too much off. This
prevents the glass from becoming vulnerable to possible breakage. Those that do post-tempering fabrication need to know what they’re doing. If the glass is altered because the grinding is 1/16th off it could change the ultimate strength of the glass. A company really needs to know what it’s doing if going outside of the standard.”

Paul Mouton, senior sales development at MWGF, says that in extreme circumstances, if the tolerance is off, his company will run the post-tempered laminated glass through a single pass on a straight line polishing or edging machine.

“It’s our last resort because with tempered glass, if you run the edge through there’s a good possibility the glass could crack,” he says.

Smith says that CGH works per ASTM C1048. He says his company feels strongly that all fabrication on heat-treated glass must be done prior to heat treatment.

“If you do any fabrication after heat treating it will reduce the edge compression and edge strength,” he says. “We will not waiver from the ASTM standard.”

Jordan Scott is an assistant editor for USGlass magazine. She can be reached at jscott@glass.com.

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