by Bob Beranek

Glass preparation is very important to the success of the bonding chain, but proper preparation of the body’s frame (the pinchweld) is equally important. In most cases we don’t actually prep the pinchweld, but we prep the bonding surface applied to the pinchweld. The bonding surface is most often the existing original bead of urethane applied by the vehicle manufacturer, but it could be the OE paint, OE primer or aftermarket primer. In any case, the bonding must be attained by following the adhesive manufacturer’s instructions exactly as written.

The first universal understanding of bonding adhesives is that an adhesive will always adhere better to itself, or its chemical twin, than to any other surface. Thus, urethane adheres better to urethane than it does to other surfaces or coatings. That being said, it is our goal to reach a pure uncontaminated urethane surface to which we will bond. Getting there is the skilled part of the installation.

Our goal should be to cut out the glass from the vehicle and strip the urethane from the body cleanly without scratching any of the painted surfaces. And, in a perfect world, all technicians would cleanly re-install the glass without any excessive urethane oozing to the pinchweld wall leaving 1-2 mm (millimeter) of original urethane by which the next technician could replicate the first installation and so on and so on. However, that is not how things are in the real world. Many times the technician finds improper prior installations, sloppy body work or corrosion that has to be treated. This means that pinchweld preparation is more difficult to attain and experienced decision-making must be implemented to correct the problem or create the proper bond.

The next series of posts I plan to share is how we deal with each of the situations that might present itself in preparation of the bonding surface. All of these discussions are in the adhesive instructions of your chosen urethane product, but I have found that the instructions are either forgotten or seldom taught because they are not followed or understood universally.

Basic Body Preparation

The basic body preparation instruction is the first one that every urethane manufacturer prints in their instructions and teaches. The reason is because it is the scenario that is most commonly seen by the technician; it is the simplest to explain, easiest in theory and most cost effective.


Remove the glass, trim back the existing urethane to 1-2 mm (1/16 of an inch), apply urethane and set the glass.


There is no need to add primer to the existing bead because urethane sticks best too itself.

Cost Effective

If there are no scratches caused, no primer is needed and cost can be reduced.


This is the perfect world scenario that unfortunately many of us see only seldom due to the issues named above. However, we should keep trying to attain this perfect bonding scenario because it is the simplest, easiest and least expensive way to go. We can increase the frequency of this basic preparation with the use of technologically advanced tools and the implementation of improved technique. Eliminate scratches and contamination and you have contributed greatly to the steps necessary to the perfect installation.

What do I mean by technologically advanced tools and improved technique? I mean the new wire-out tools, power tools and how they’re used, and special cold knife blades all contribute to less body damage. Strip out tools and the techniques in stripping the urethane from the body also reduce the chance of paint damage. Less body damage means less additional preparation is needed for bonding and more profits are realized due to increased productivity.

Next week we will look at the more challenging body preparation issues.

On this the first post for 2014, I would like to thank everyone for reading and commenting on my posts, without you this blog would be nothing. I would also like to thank Deb Levy and her wonderful staff for putting up with me these past months and for the opportunity to share my thoughts and opinions without restrictions.

The New Year will bring many new vehicle designs, technologies and challenges that we will tackle together. Feel free to call or email me with your questions, concerns or revelations that can be shared with all. This next year will be fun. May you all have a happy and prosperous New Year!

The next step in glass preparation is prepping or priming. There are primerless urethanes and they work very well as long as the glass is cleaned properly. However, if not cleaned properly, the installation could be compromised. Most adhesives require the application of a prep or a primer to promote maximum adhesion. A prep is a secondary cleaner or application to prepare for adhesion. A primer is a chemical applied to a substrate to enhance the bonding. Whether a prep or a primer is required to be applied, it must be applied correctly. Some are applied and allowed to flash. Some are applied and wiped off, while some are applied twice. But all must be applied in one direction and not applied back and forth.

There is also a reason that some adhesive manufacturers offer “one-use” disposable applicators. They want the material to be applied with as little contamination as possible. There are some techs that use and reuse applicators to save installation cost. Though this may sound like a good idea, it is not. Introducing contaminants to the bottle of material will only cause the whole bottle to be contaminated. Dip once, apply and throw away.

The last thing I want to leave you with concerning glass preparation is when should you prep the glass? The following is my opinion and recommendation. It is not written in any instruction manual. I prefer to prep my glass before I take the vehicle apart. This allows me to inspect the glass for defects; check the glass to make sure it is the proper part for the vehicle; and let the primer/preps dry thoroughly. I then flip the glass over on my cradle to keep airborne contaminants from falling on the bonding surface. On cold days, I may even prep the glass in the shop before doing the mobiles. This allows for preparation in a controlled environment and allows primers/preps to dry thoroughly but this means you bought the glass, so make sure the glass is right.

In summary, if there is one thing you pay attention to and make sure is done right, it is to wash and prep the glass according to the instructions you are given. Nothing is more important to a successful and safe installation than a properly prepped glass surface.

Preparing for the installation is the step where many technicians make their biggest mistakes. The removal and installation steps, where skill and experience are demonstrated, are the parts every tech brags about. However, preparation is what separates the men from the boys. This is where the bonding begins and the mistakes happen.

There are three sub-sections to the preparation step: glass preparation, pinchweld preparation and preparing for the installation of the glass in the opening. Today we will deal with the first part of glass preparation, making sure the glass is free of contaminants.

Chemists tell me that improper cleaning of the glass surface is the number one reason for adhesion failure of the glass to the body of the vehicle. This can be caused by the wrong glass cleaner, the wrong wipes, the wrong handling of stubborn contaminants, or the procedure itself.

The first rule should be to use the type and brand of glass cleaner recommended by your adhesive manufacturer. Doesn’t it make sense to use products that have been tried and tested in the lab? At the very least follow their recommendations as to what criteria is important in selecting a glass cleaner.

Glass cleaners should not contain ammonia, excessive alcohols, anti-static properties, scented oils, silicones or petroleum byproducts. I have found that foaming glass cleaner is better than non-foaming because it helps find oil based contaminants by dissipation of the foam upon application. Whatever cleaner you choose should be discussed with your adhesive rep to make sure it is compatible with your urethane.

Use disposable wipes, not shop towels to wash the glass. Towels may seem more cost effective, but the result is an ineffective bond. Remember that shop towels are washed by the towel service with other towels from other customers. The other customers could be mechanics shops, oil change centers or collision centers. They are washed with harsh chemicals to clean them. Once you add a cleaning solution to the glass and wipe with a shop towel, some of these chemicals are released and applied to the bonding surface thus hindering adhesion. The best cleaning wipes are good old disposable paper towels that are used once and thrown away.

What about the stubborn tape residue or manufacturing release agent used in the encapsulation process? How do we get that off or do we have to? There are now abrasive materials available to remove these types of contaminants. I strongly suggest that you use these products and follow manufacturers’ instructions carefully to best prepare the surface for bonding.

All customers like clean and shiny windshields but don’t forget that the bonding edge is the most important part of the glass to clean, not the transparent center. We can always shine it up after the installation. The wipes are never as clean as when taken from the roll or box. This is why we clean the edges first. The procedure for cleaning the glass is as follows:

—Spray the edge with foaming glass cleaner and notice any dissipation of the foam. If there is some dissipation, scrub that areas of dissipation firmly with a clean lint-free paper towel and re-spray the area again to test.

—If there is additional dissipation or other residue present, utilize the product or procedure recommended by your adhesive manufacturer. This can include the application of an abrasive cleaner or wet scrubbing of the area or both.

—Once the edges are free from contaminants wash the remainder of the interior surface from the edges to the center.

—Make sure that the edges are perfectly dry before application of primers or preps.