by Bob Beranek

Photo Courtesy of

I can always tell when a technician was trained by an “old-timer” like me. How? They “spank” or slap the glass into position rather than smooth it in place to make the seal. It comes from the old days when glass had to be spanked and seated into a gasket or when dense butyl tape needed to be forced down to contact uneven pinchwelds. Liquid urethanes call for smoothing the seal, not spanking or slapping the glass into place.

First, let me say it’s not necessarily wrong to slap the glass. It is, rather, ill-advised. There are two negative results that can happen when a glass is slapped rather than smoothed.

  • If the glass is thin, chipped or scratched, then the chance of premature breakage is increased. If the glass is “hot,” the glass is more volatile and can fracture. Some of these issues can and should be caught by the technician prior to installing. However, how hard is too hard to slap the glass into place? It only takes one break to lose your profit and possibly a customer to inconvenience.
  • The second negative issue involves leaking and bonding. Curved glass has a spring to it. It can be depressed as much as a couple of inches before breakage and then sprung back to its original shape or curvature. If the bead of urethane is short and the glass is slapped at its apex, it can make contact and then “string out,” causing leaks and bonding problems. If it is smoothed-out, the urethane bead is redistributed into weak areas, making for a more solid bond and leak-free installation.

If I said I never spanked or slapped the glass, I would be a liar. There are instances where a slight slap is necessary. If you have a large, tall or awkward vehicle where leveraged pressure can’t be applied to the edge of the glass, such as in large service vans, then a slight tap on the top and bottom center may be called for. Of course, this is after a careful inspection of the glass part conducted during the prep stage and that the glass is not exposed to excessive heat.

My advice is to use slapping only when you must and only when the glass was carefully inspected for pre-installation damage. Keep the glass out of bright hot sunlight for as long as possible prior to installation into the opening. Reduce the violence used in past installations as much as you can. The customer will feel less anxious if watching the process and vehicle and glass damage will be reduced to increase profits.


Recently I was surprised to hear one of my colleagues had never heard of the term “decking.” That instance got me thinking, glass techs do speak a language of their own. A good example is from previous Education Committee debates, where I learned there are a lot of colloquial names for plastic sticks like, bones, fiber sticks, and the always popular “pooky sticks”; different terms were used based on the location.

I thought it would be beneficial to start a glossary of terms and add them to the dictionary of auto glass terminology. Here are some to start:

  • Decking

Decking refers to the act of pressing the glass downward into its final position on an applied adhesive. A common phrase would be, I decked the glass into position on the pinchweld.

  • Pinchweld

Considering this term doesn’t exist in my computer’s dictionary for some reason, I thought it might be added to our glossary for that reason alone. Everyone knows what a pinchweld is, a periodic weld between two layers of metal.

However, in the auto glass industry we look at a pinchweld as not just a thing, but as an item with multiple parts. It can be “L” shaped, “flat” or have a “Z” shape. It can also have a “floor” and a “wall.”

It’s a part of the vehicle frame that a glass part is adhered to.


  • Exposed-edged Part

An exposed-edge glass part is any glass part with an unprotected edge. It can still have an underside moulding attached, but the very edge of the glass is exposed.


  • Bead

The bead is an extrusion of the urethane adhesive, and is usually found on the under edge of the glass part. However, it can also be recessed on the bottom of the glass. Sometimes the bead is applied to the glass and other times applied to the vehicle frame (pinchweld).

  • Cowl

The true term for the “cowl” is the cowl panel. It’s a cover located at the bottom edge of the glass and extends to the front of the firewall. It covers the cowl/firewall drains. The panel usually surrounds the windshield wiper posts and covers the unsightliness of the drains and raw metal underneath. The cowl panel should be removed on most vehicles to perform a proper installation.

  • Tucking

Tucking is the act of inserting the glass under the cowl panel without its removal. Tucking can displace the applied adhesive and make the glass installation unsafe. It is usually used to save time removing the cowl panel and wiper.


These acronyms stand for Safe Drive Away Time and Minimum Drive Away Time. They have been used interchangeably, however the industry wants to begin using the later. To reach MDAT the urethane must reach the strength necessary to withstand the forces put upon the glass as defined in Federal Motor Vehicle Safety Standards 208 and 212. The titles of these standards are Passive Restraint Systems and Windshield Retention respectively.

These terms are only the start. If any of my readers have heard a term used they are not familiar with or if you have some terms we should add, please let me know.

I belong to several glass related technicians’ groups on Facebook and enjoy participating in discussions when I can. This past week a conversation brought back memories of my installer past and the old DW837/836 windshield. I thought I would share it with my readers this week.

The DW837/836 windshield is the windshield for a 1975-1991 Ford full-sized van. Back in the day, we used to do a LOT of them. That was our service vehicle when I was an installer. It has four-sided heavy chrome mouldings and a block size of 34×73, which makes it a large and awkward piece of glass to set by yourself. The original equipment adhesive was butyl tape.

Photo Courtesy of Purple Wave

When I did these windshields, we used round butyl to replace them. I would smear some liquid butyl on the passenger side bottom pinchweld and apply the butyl tape to the glass. Then, I set the glass onto the liquid butyl, slid it to the far pinchweld, set it in place, decked it and then back sealed the seam with a flow-grade sealant. This was a successful method because we rarely had a leak or noise complaint. The two types of butyl meshed together and sealed permanently.

Our Industry Standard says:

8.4 Whenever OEM retention systems are modified on later production models without body style modification, the most current retention system shall be used in the replacement unless otherwise specified by the OEM.

However, the Ford van never had a change to urethane until the body style changed in 1992.  Thus, the OEM specifies butyl for a Ford Van of that body style so by rights, butyl could be used.

Today our industry recommends the use of urethane when replacing these parts, rather than continuing to use inferior bonding adhesives. This is to ensure the bonding is improved and not hindered and so the replacement must be done correctly.

One of the biggest challenges for field techs is that urethane and butyl are not compatible for bonding purposes. This means ALL of the butyl must be removed for proper bonding. Unfortunately butyl tape is difficult to remove, especially if the tape is older. You then must scrape off the biggest share, and continue with one of the following to remove the rest without damaging the paint:

  • Use a sharpened plastic stick to scrape off the remainder of the tape.
  • Use a big ball of old butyl to stick to the remaining butyl and peal it off.
  • Use a solvent for removal. This would require an additional process to neutralize the solvent.

In any case, it’s time consuming and difficult to accomplish.

In a past posting I suggested the use of a tool used by collision centers to remove decals and pinstriping, called an eraser. It’s a rubber wheel inserted into a drill and used as a butyl eraser; it works well. It literally erases the butyl like pencil markings from paper without damage to the paint. The tech then dusts the pinchweld of rubberized residue, primes the pinchweld, applies the urethane to the proper height and width and sets the glass using the modern setting tools or a helper.  

This method of butyl removal is fast, easy, economical and damage free. If you give it a try you won’t be sorry.