by Bob Beranek

I shouldn’t have to convince any of you which is the better bead application for auto glass adhesive, but just as I thought that every one used the “V” bead, here comes a video to prove that the round bead is alive and well in the realm of auto glass installation. The video I’m talking about is the video that has been broadcast by KVOR in Sacramento on the program Call Kurtis Investigates In it, the installer uses the round bead and the technique of holding the gun above the pinchweld and laying it in place as a means of applying the urethane to the vehicle. It is for “show” and not for the good of the installation.  I have seen this all over the country and the technique is meant to impress the watcher and, as misguided as it is, to show how talented the installer is.

The history of round beads goes back before the windshield’s role changed in 1973. In the good ol’ days, there was no urethane, only butyl tape. Butyl tapes were sold in round and rectangular shapes. Most installers at the time used the round shape because it sealed better and water leaks were less likely to occur. Then, when urethane was introduced in tubes with tapered cone-shaped tips, the obvious dispensed bead would be round.

Once the urethane adhesives became the norm in auto glass adhesion, the proper application procedures were then taught from vehicle manufacturers, adhesive manufacturers and training professionals. Adhesive manufacturers even started putting pre-cut “V” tips in with their products. That didn’t stop the old timers. They just cut off the tip down to the round portion of the tip and applied their round bead just like before. No matter how much you told them that the “V” bead was better, they didn’t want to hear it.

I remember a training course I gave where one of my students demanded that the round bead was better. He said he had done hundreds, if not thousands, of installations with round beads and “he never had a problem.” Sound familiar? He even bet me a beer that his way was better than the “V” beaded. Well, you know where this was going. During the hands-on portion of the training, we tried my way of applying the bead and his way. Then we water tested the installations and, lo and behold, his installation leaked in three spots and mine did not leak at all. He also used almost twice as much adhesive as I did. That beer sure tasted good.

The “V” bead is almost a fail-safe way of applying adhesive. As long as it is high enough it can be wobbly or crooked, but if the tip touches the underside of the glass, it will seal and bond.  Plus, the triangle morphs into a perfect sealing rectangle when properly decked.

The most important part of using a “V” over a round bead is the increased bonding between the two surfaces. Let me illustrate with some relatively simple pictures.

When a round bead is used the round shape can only be made into an oval shape. Notice the area of bonding on figure 1.

The “V” bead when applied maximizes the bonding area and does not change with the pressure of decking. Notice the area of bonding on figure 2.

Here are the procedures for applying urethane to either the glass or the pinchweld.

  • Cut or adjust the “V” bead to the proper width and height.
    • Cut the tip to be the width of the existing OE urethane bead. Do not cut the tip at a 45 degree angle. This will not allow for proper application.
    • Cut the “V” equal to and slightly greater than the height of the wall of the pinchweld. Use the top “L” shaped pinchweld to make your measurements. The side (“A” pillar) pinchweld is not consistent and may give you a false measurement.
    • If you are applying the bead to a clipped moulding style vehicle, cut the “V” bead equal to or slightly higher than the height of the clip. Then set the glass and use the mouldings as a measuring device and decking device at the same time. While you push down with the mouldings to engage the clip you are simultaneously decking the glass to the proper height. Once the clip is engaged, stop pushing down on the glass. This will eliminate a gap between the glass surface and the moulding.
  • Apply the urethane with the caulk gun positioned 90 degrees to the surface (perpendicular). This causes the adhesive to be applied to the surface and not laid on the surface. Laid adhesive can cause leaks because it can bridge gaps or depressions on the surface. Applied adhesives assure that any imperfections on the surface are filled and the “V” is facing upward ready for the next surface to meet it.
  • Before setting the glass make sure that any seams caused by the application are paddled together and a “V” shape is replicated.

If you out there are still using the round bead, stop. I guarantee that your callbacks will be reduced when you properly use a “V” bead application.

Comments (7)

  1. Daniel said on 26-06-2012

    There would be, though, some situations that would receive round urethane bead rather than triangled section. I would give the situation you have curved lites, with relatively small curve radius. Say the rear glass of Mecedes A-Klasse type 1–and you, the readers of this comment may add other examples. Deposing a higher triangle bead will result in a final displaced adhered perimeter, inside or outside the designed line, depending on the solution you choose for laying the urethane (on the glass or onto the pinchweld).
    I will let you have another situation I often encountered when practicing in Lorton,VA which I find at least hilarious if not dangerous. One of my team mates was not cutting the old urethane down to 1-2 millimeters from the pinchweld. The old adhesive left onto vehicle was at least 5 millimeters. He disposed then a tiny (3 millimeters) round worm of fresh urethane onto the old bead and applied the new glass. No need to enhance the adhesive spared !
    But if for a side glass (vent) or even rear glass that would do, in the windshield area I would never agree with that. He argued with the same line “I’m doin’ this for decades, and no complaint was registered!” Hope — for his own and only benefit– the day he will get his a** kicked, because of a weak bond won’t arrive so soon.
    Bottom line: I never saw any round urethane beading, nowhere in the workshops I have practiced in Europe.

  2. […] it puts a V shaped bead like this. You cut the tip like this. Here is a site explaining why. Round Bead v. You set the glass onto this bead and press it down a bit and wham, you have a windshield […]

  3. Jason C. Davis said on 18-10-2012

    I run both beads, I have been doing this for 18 years. It just matters what you are working on and the depth of a pinchweld. Sometimes it is hard to run a v-bead on some of the crazy designed deep pinchwelds , especially with a heavy caulk gun. I run both beads very well and I don’t have any problems.

  4. John R. Allen said on 07-03-2013

    Round beads, I can’t belive we are discussing this again! 99.9% of the poorly installed windshields we see on a daily/weekly basis is all round beads! The round bead is not high enough to compensate for the weld indents in the pinch weld, thus causing wind noise and water leaks. The factory uses a V bead, EVERYONE should as well!

  5. Daniel McDonald said on 09-11-2016

    I support “V” beads 100%. I was trained in my first 2 years of my ongoing 13 year career, to run round beads. Then once moving my career to safelite autoglass I was proposed to run a “V” bead. It took some time to gain confidence in it, but now that’s all I apply on any adhered glass. It’s turned into a mandatory policy here and we have far less warranty issues with leaks and air noise caused by round beads. If you aren’t trying it then you need to start now. It’s the only way to safely bond a windshield in my professional opinion.

  6. Edwin said on 30-11-2016

    How exactly do you cut a V into the tip? Do you cut into the standard round tip that it comes with or do you have to get a triangle shaped tip? Not really sure what to do here…

  7. Ashley Johnson said on 05-07-2019

    I liked that you said that one of the best ways of performing tube beading is by creating the “V” bead. It made sense when you explained that this is the fail-safe way of applying adhesive in order to create a perfect sealing rectangle. I would be sure to hire a professional who does this work effortlessly in order to achieve quality.

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