Applying Urethane

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.