by Bob Beranek
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I’m dedicating this post to “setting the glass.”

What exactly is meant by setting the glass? Setting the glass refers to placing the glass into the opening on the vehicle’s body where it is meant to fit. Some glass parts are adhered to the frame (pinchweld) and others are mechanically fastened and attached with nuts and bolts. The adhered part uses adhesive to bond and seal the opening from weather related issues, while the mechanically attached parts use a sealant.

Proper glass setting is imperative to sealing and bonding success. The amount of clearance in many cases, from top to bottom and from left to right are less than ¼ inch. The most important and difficult part to set and manipulate is the windshield. Due to its size, awkwardness, and importance to safety, the windshield gets all of the attention when it comes to accurate placement.

To properly set a glass into an opening, it is imperative to have access to all sides of the glass part and the opening. Tucking the glass under the cowl panel is not an acceptable procedure.  The technician cannot see the lower bead contact the adhesive and cannot correct a displaced bead after setting it because of the cowl panel’s presence.

There are many procedures and tools available to aid in setting the glass. Some may take extra effort, more practice, or additional cost than others, but the choice is that of the technician.

Once the glass is set in the opening and on the adhesive, the next step is to “deck” it out and make the seal. This is accomplished by the firm but gentle depression of the glass into the opening. How far into the opening the glass is depressed is important, if it’s too far and the glass could be susceptible to stress cracks. On the other hand, if it’s too little, and the glass will not perform its safety role in a crash.

The ideal positioning in the opening is dependent on the style of the vehicle. In a vehicle equipped with exterior mouldings the outside glass surface should be tight against the underside of the exterior mouldings and spaced high enough from the interior mouldings to prevent unpleasant noises.

If the glass has an exposed-edge style of mounting, then the glass positioning should be slightly lower than flush with the roofline. If it’s flush with the roofline, the glass and body can cause a noise called the “flute” effect. The air blows over the gap between the glass edge and the wall of the pinchweld causing a whistle or air rush noise. If the glass is too high, then the windshield will not support the roof to FMVSS 216a required for safety. If the glass is decked too low and the glass loses its freedom of movement and can cause stress fractures.

Setting the glass is vital to the success of the installation and must be accomplished flawlessly every time. Do not take shortcuts with this step.

Recently we’ve seen an increase of original equipment (OE) glass purchases from dealerships. Why, because Advanced Driver Assistance Systems (ADAS) are being incorporated into new vehicles more often than not. This means auto glass companies that don’t recalibrate ADAS systems must depend on dealerships. By adding dealerships as a partner to complete auto glass services for their mutual customer, may mean the dealership will demand OE glass be obtained for the replacement to facilitate recalibrations.

What does that have to do with the title of this post? When OE glass is purchased from a dealer, it can sometimes come to auto glass shops pre-primed, especially if the vehicle is a new model or has just been manufactured for the new model year. This can pose a problem if the urethane adhesive you choose doesn’t allow use with unknown primers.

We all know technicians should never use a glass part with an unknown primer applied. If glass is delivered to your shop and the glass has a primer applied, it should be returned for a new part. The technician wouldn’t have a way of knowing how the glass was cleaned, primed, or prepared and what chemicals were used. You also wouldn’t know if the glass was cleaned properly and if the primer used was compatible with the primers the technician will use? None of these things are known and no one should assume the previous technician knew what they were doing when they prepped the part.

You may think, I’ll just clean it off, but will you, and can you? It may look clean and contaminant free when you’re done cleaning it, but is it really? If you use abrasives to remove any foreign materials some of the frit paint may be removed. The frit is a rough surface with peaks and valleys that are coated with chemicals that can’t be removed fully without removing a substantial amount of the frit paint. When frit paint is removed the frit is not as protective of the urethane as it was before. The adhesive will be more susceptible to ultraviolet light breakdown and reduction in mechanical bond.

So, what should we do to prep the pre-primed OE part? I asked that question to three of the top auto glass adhesive manufacturers’ in the industry. Unfortunately, each had a different answer, but none said you can’t prep an OE part properly with the right procedures. One of the top adhesive producers warned not all OE prepped glass was equal in terms of proper priming. OE’s make mistakes like everyone else. I’ve previously written about problems with priming that must be addressed if witnessed.

I urge all technicians and owners that read this article, to check with their adhesive representatives or check their adhesive instructions to verify the procedures in dealing with pre-primed OE parts. If your urethane of choice has neither a rep nor written instructions covering this issue, the only way you can be assured the primer on the OE part is compatible with the urethane used is to purchase the OE urethane kit with the OE glass part. Then follow the written instructions given to you by the OE adhesive company.

Last month I wrote an article on the terms used in the industry by auto glass professionals.  Today, I’m continuing it.

Plunge-cut – A plunge-cut has both a negative and positive connotation. It’s been seen negatively when it is used as a method of easing the use of a cold knife. The belief was that if you cut along the glass’s edge with a utility knife, the vertical cutting edge of the cold knife blade would be less of a drag on the tool, thus making it easier to pull. However, it would also score the floor of the pinchweld and cause oxidation to occur and undermine the urethane bead.

The positive connotation: it’s a technique to remove the flap of a “J” style moulding. Removing the extending flap makes it easier to remove the remaining portion of moulding and makes the cold knife cut smoother without hindrance. The trick is not to plunge the knife blade too deep where it contacts the pinchweld floor.

Gravity Stops – It’s the modern name for devices that support the bottom of the glass part and stops the glass from sliding off of the adhesive. Now, the OE manufacturers’ other means to support the glass while the adhesive cures that will do the job and not cause squeaking. The cowl panel is one method and additionally they use guide pins or hangers.

Guide Pins/Hangers – These are OE parts used by robotic machines that set the glass into place during assembly. You rarely see these parts used in the aftermarket, because they are usually located within about 8-12 inches from the top corner of the glass part and are held in place by double-sided tape or silicone adhesive. These guides serve two purposes: it helps the robot set the glass and keeps it in place until the urethane adhesive cures to its ultimate strength.

The above description does illustrate the use of guide pins in windshield mountings. However, there’s another use for guide pins when discussing other auto glass parts. Some side parts have a tilt-out style of mounting, like in quarter glasses and vents. These parts also use an extended “guide pin” that is threaded and used to attach the hinge to the vehicle frame. It’s also called a “T” bolt. These extended threaded bolts are usually a part of the hinge and helps the robot insert the part into the pre-drilled holes in the frame’s body. Then a nut is used to securely attach the part to the body.

“T” Bolt – “T” bolts are guide pins embedded into a plastic moulding around a glass parts’ edge. The extended bolts are used by robotic machines to set the glass part into place and to attach the glass part to the body.

Encapsulation – Encapsulation is a process where a glass part is placed into a mold and molten plastic is pumped into the mold to create a part where the glass and moulding become one.  Because the encapsulation is either PolyVinyl Chloride (PVC) or Reaction Injected Molded (RIM) plastic, the adhesives used to adhere the glass part to the body may need help to stick properly. That’s why the encapsulated parts are frequently equipped with “T” bolts embedded into the encapsulation or clips that hold the part in place until the adhesive cures.