Last week we looked at tool options for trimming back the urethane bead to the level suggested by the adhesive manufactures (1/16^th on an inch) when replacing a windshield. This week we’ll address the procedures that must be employed to make sure the glass is solidly bonded and the installation is leak-free.

If you use a razor blade style tool, the strip-out may not leave you with a 1/16-inch buffer. Used properly, it will usually take the bead right down to the painted surface, leaving only a trace of existing material. If the blade angle is too high, then the paint is damaged and more priming is necessary. However, if the tool is used to “shave” the urethane from the metal, scratches will be minimal but so will the existing bead. Is this wrong? You may think so if you are the one going back on a second or third installation. There is no easy way to get to the OE bead if some is not left behind from the first installation.

If you use a scraper tool like a chisel, then I would suggest to turn the chisel with the beveled side facing down to the metal. Using the tool in this way leaves a 1/16^th-of-an-inch-of old urethane, strips off the majority of the rest and reduces the chance of damage to the metal. This requires a little more effort by the technician but it does leave behind the amount of existing urethane that is called for by the adhesive companies. It also makes it easier to reach the OE bead on the second or third replacement.

Any tool you use to strip the urethane must be sharp. If you have a razor blade tool, change the blade on every strip-out. If you have a utility blade style of tool, use one side of the blade for one vehicle and then the opposite side of the blade for the next. Chisel style blade tools must be kept sharp and honed between installations. I used to sharpen them on a grinding wheel or a wet sander every morning and then hone them before every install throughout the day.

When using a long-handled utility knife to strip the bead, some technicians will hold the tool with two hands and strip the urethane. The problem with this method is that if there is a defect in the bond, such as paint delamination, the blade can skim over the defect and the problem will escape detection. If the technician starts the strip-out and then pulls and stretches the removed bead with one hand while he uses the tool with the other hand, a defect will show itself and the technician can then deal with the problem.

Once the adhesive is removed, the next step is to make sure the existing bead that is left behind is ready for the application of the new bead. DO NOT touch the freshly exposed bead if you can help it. If you must touch it, change your gloves from safety gloves to new nitrile gloves so you will not contaminate the existing bead. Check for some uniformity in the existing bead you are bonding to. If there are real high or low points, the glass could fracture upon setting. Next, check for any scratches or gaps in in the bonding area. If there are some present follow the adhesive company’s detailed instructions for primer application.

Lastly, check the old bead for “flaps” in the bonding area. What I mean by “flaps” are overlapping slivers of urethane laying on top of one another. They are very hard to see sometimes but they have to be eliminated. If a fresh bead of adhesive is put over a flap, then the seal will leak at that point and the bond compromised.

Master the strip-out and you will reduce your installations times by several minutes.