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.


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.

When installing a windshield, do you lay your bead of urethane or do you apply your bead of urethane? Perhaps you are thinking, “What is the difference?” Actually, there is quite a bit of difference. I heavily favor “V” beads over round due to the better bonding and sealing dynamics. I apply the adhesive bead to either the glass or the pinchweld, depending on which type of glass part I am doing, or if there is an existing OE bead for me to follow. However, applying the bead to a surface is very important to the success of the installation. (Please note: Always reference your adhesive manufacturer’s instructions to determine the type of bead that should be used.)

Today I want to discuss the proper way to apply the adhesive bead to whichever surface you choose. How many of you have seen an installer hold his caulk gun six inches off the pinchweld to lay the round bead to the surface? Over the years I have seen this several times and have always wondered why. So I asked. Believe it or not, more than one technician has told me it was because they thought it was “cool.” They told me that the customers who watch them do the installation thought that the way they laid their bead was very professional and somehow instilled an air of confidence in the installer’s skill. Wow, are you kidding me?

Applying the bead of urethane is probably the most important part of the installation process. The type of bead and where you put it is imperative to the success of the bond and seal. Take a look at this video. The interesting part is at the 3:00 minute point.

This video is a perfect example of what I am talking about. This is not only wrong, it is dangerous to the owner/occupant. The right way to apply a bead of urethane is to apply it and not lay it.


What I mean by apply is to cut your “V” bead the width of the existing OE bead and equal to the height of the upper pinchweld wall and then apply the bead while holding your caulk gun in a 90-degree angle to the surface (perpendicular) and pressing the nozzle down to touch the surface. This applies a tall straight “V” bead that fills all gaps and assures proper adhesion to the surface.

Laying the bead like in the video above or even at a 45-degree angle to the surface can cause a weakness in the adhesion or bridge a low spot which could cause a leak or bond problem.

Now you’re going to say, I can’t always get my gun at 90 degrees because the vehicle is too tall or the opening is too big. I realize that. I am six foot two and I have problems reaching the large and tall vehicles as well. Sometimes getting your gun at 90 degrees is impossible. However, if that vehicle is so big that you can’t reach the top middle to apply at 90 degrees°, at least reach as far as you can and get the gun perpendicular as soon as possible. Or, apply the adhesive to the glass and use a setting tool or another person to assist in the set.

The point is to apply the adhesive bead to the surface making sure that the seal and bond is secure. Don’t lay the bead with the hope that the liquidity of the adhesive will find the gaps in the surface you are laying it on. Simple tasks mastered make for great technicians.