by Bob Beranek

Last week we looked at tool options for trimming back the urethane bead to the level suggested by the adhesive manufactures (1/16th 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 1/16th-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.

09152016bobWhen 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.

One of the most difficult skills a new technician needs to master is how to trim back the existing urethane to the proper point. The typical advice, used in the industry for decades, is to trim the existing bead to 1-2 mm or a 1/16 of an inch. Though we have all heard this phrase used frequently, most people don’t trim back the existing bead and then measure the thickness of the urethane left behind to make sure that it was exactly a 1/16th of an inch. If the bead is a 1/32 or 3/16 of an inch, is that wrong? No it is not.

The purpose of leaving some existing urethane is twofold. The most important reason is to discourage the technician from going too close to the painted metal and thus damaging the pinchweld and causing corrosion. The second reason is to remove most of the aged and possibly deteriorated urethane and to leave behind a perfect virgin bonding surface for the new urethane to adhere to. Both of these goals are important to the success of the bond and the protection of the vehicle, but the exact amount of the existing urethane to leave behind is not as important as the end result.

The bottom line is don’t damage the pinchweld, and be sure to remove most of the old bead. I frequently see new technicians struggle with this directive, prolonging the installation process or causing the quality of the installation to suffer.

In the next few of posts I will address the proper procedures for full strip-outs and the ramifications when the strip-out is done incorrectly. Today, I will address the tools available for this purpose.

There is a wide array of tools to perform the act of stripping the old urethane from the body. Some of these tools are commonly found in a hardware store for affordable prices. Others bring highly sophisticated designs that make the task easy and reduce the chance of damage. However, with practice and care, they all work fine. I have yet to stop a technician from using a tool they have success with. Yes, I do have my preferences, which usually are formed by the length of the learning curve but there are arguments for and against for every tool I’ve seen. Here is just a small list with my comments:

Razor Blade Scraper: These are inexpensive. It is a single-edged razor blade that can be changed often for little cost. Once learned, it is easy to use. The blade can be too wide for the average pinchweld. The tool can strip too close to the body and the blade is sharp and can easily cause damage until mastered.

Utility knife/Long-handled Utility, Olfa® Knife: These are relatively inexpensive. You must use the proper knife blades or the blades can snap. Some blades can be a little more expensive. It takes more practice to learn and master this method. The tool can damage headliners and interior garnish mouldings. It can also strip too close to the body. The blade is sharp and can easily cause damage until mastered.

Scrapers, Chisels, Putty Knives: These are relatively inexpensive. The blades need to be sharpened and kept honed for productive use. If used incorrectly, the blade can cause paint damage. It is a little harder to use than replaceable blade-type tools.

Replaceable Blade Scrapers: These are sometimes called “inline” utility knifes. These use the action of a scraper and the replaceable blades like a utility knife. They are medium-priced. The blades can be expensive in comparison to utility blades but they can be sharpened and reused. Multiple blade widths allow for use on any sized pinchweld.

Pinchweld Prep Tools: These tools are specifically designed for automotive glass installation and they vary in style and use. They can be expensive, but they have protections built in to reduce damage to the vehicle and usually provide a short learning curve.

There are technicians getting excellent results with all of these tools. It is worthwhile to take the time to figure out what works best for you. Remember, the key is to get a smooth, damage-free removal of the existing bead, leaving the virgin surface for the proper bonding of your new urethane.

The introduction of the exposed-glass mounting has led to a paramount concern for installers not to damage the exposed pinchweld wall. If the pinchweld is damaged during installation, and priming exceeds the underside moulding weather mark, there is a real possibility that our customers will not like the look. This has changed the way we remove the glass and even introduced a new type of tool, the wire-out tools.

Many glass parts now are designed with an exposed edge. Some are exposed on all sides and some are only exposed on the top of the glass part. Some show the wall and the floor of the pinchweld, and others have an underside moulding that replicates the PAAS windshields of the past.

Let’s address the underside moulding installations specifically as it relates to bonding.

The underside mouldings are held in place with a strip of double-faced tape. It is applied to the inside surface edge of the glass. It is used, like all mouldings, as a decorative finishing touch. However, if the underside moulding is not taken into consideration during the installation process, the bonding of the glass to the body of the vehicle can be compromised.



There are a couple of procedures that can improve the odds of safe bonding:

  • Bead application. Make sure, when applying your bead, that the tip of the “V” bead is perfectly perpendicular to the floor of the pinchweld. If it is pointing outwardly, it will make contact with the moulding and not the glass surface. This will not only create an unsafe bond but it will also cause a moulding appearance problem and a clean-up nightmare. If there is an acceptable variant in bead application, it would be that the bead be slightly tilting inward, but 90° to the floor is better.
  • Set the glass top first when possible and set the glass high. What I mean by that is to set the glass higher than the opening and then bring it down into position. In this way the “V” bead will catch the underside of the glass and not the moulding. As the glass is brought down, the bead is in position to safely bond the glass to the frame. The bead is pushed up against the inner edge of the moulding but on the glass surface and not on the moulding.
  • Apply the new urethane bead directly on the existing original bead. If corners are cut, or if the bead deviates from the original bead even slightly, the result is the bead contacting the moulding and not the glass surface. It also can result in adhesive oozing outward causing the moulding to pucker and appearance to suffer. You may need to slow the application of the bead to assure accurate placement. This is hugely important to the success and acceptability of the installation.

Exposed-edge glass does provide for an attractive appearance. It reduces drag for more fuel efficiency. However, it is a blind-set installation. We cannot see the bond being made. We have to depend on our bead configuration, size and position to assure proper bonding and leak-free performance. So, make sure you pay attention to the bead application and the setting procedure. We cannot afford to be sloppy in our procedures with these types of installations. There is no room for error.