by Bob Beranek
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Keeping up with my theme of addressing the glossary of terms, this blog is dedicated to the most important term of all – frit. Why do I say it’s the most important? The answer – its importance to bonding glass to vehicle frames and the longevity of that bond.

The frit is the black paint band around the perimeter of an auto glass part. Though it does provide the appearance benefit of acting as a “moulding” substitute to cover the urethane bead, it also has a practical purpose.

For example:
• The black color protects the polyurethane adhesive from one of its biggest enemies, ultraviolet light. Ultraviolet light is found in sunlight and it attacks urethane by breaking it down to a “caulk like” black powder. This weakens the urethane and reduces its bonding strength.

• The application of the frit paint on the number four surface of the glass adds to its adherence by adding more surfaces to bond to through mechanical adhesion. The rougher the surface the more mechanical bonding can occur.

Back when frit wasn’t applied by the glass manufacturer and urethane was used to bond glass, we applied a “black-out” primer to serve the purpose of the frit. The black-out primer and large, wide chrome mouldings protected the urethane bead from ultraviolet light and the primer acted as the roughened surface for the mechanical bond. Then glass and vehicle manufacturers realized they could add more protection and better bonding by adding frit paint to the glass.

The frit allows for “exposed edge” glass parts, which contribute to eliminating mouldings. The frit also adds more of a mechanical bond, which strengthens the safety devices the glass contributes to, and it makes the car look good.

So, pay attention to that black paint called the frit. It is important. It is not just there to make the vehicle look good. It is there for safety purposes.

Recently we’ve seen an increase of original equipment (OE) glass purchases from dealerships. Why, because Advanced Driver Assistance Systems (ADAS) are being incorporated into new vehicles more often than not. This means auto glass companies that don’t recalibrate ADAS systems must depend on dealerships. By adding dealerships as a partner to complete auto glass services for their mutual customer, may mean the dealership will demand OE glass be obtained for the replacement to facilitate recalibrations.

What does that have to do with the title of this post? When OE glass is purchased from a dealer, it can sometimes come to auto glass shops pre-primed, especially if the vehicle is a new model or has just been manufactured for the new model year. This can pose a problem if the urethane adhesive you choose doesn’t allow use with unknown primers.

We all know technicians should never use a glass part with an unknown primer applied. If glass is delivered to your shop and the glass has a primer applied, it should be returned for a new part. The technician wouldn’t have a way of knowing how the glass was cleaned, primed, or prepared and what chemicals were used. You also wouldn’t know if the glass was cleaned properly and if the primer used was compatible with the primers the technician will use? None of these things are known and no one should assume the previous technician knew what they were doing when they prepped the part.

You may think, I’ll just clean it off, but will you, and can you? It may look clean and contaminant free when you’re done cleaning it, but is it really? If you use abrasives to remove any foreign materials some of the frit paint may be removed. The frit is a rough surface with peaks and valleys that are coated with chemicals that can’t be removed fully without removing a substantial amount of the frit paint. When frit paint is removed the frit is not as protective of the urethane as it was before. The adhesive will be more susceptible to ultraviolet light breakdown and reduction in mechanical bond.

So, what should we do to prep the pre-primed OE part? I asked that question to three of the top auto glass adhesive manufacturers’ in the industry. Unfortunately, each had a different answer, but none said you can’t prep an OE part properly with the right procedures. One of the top adhesive producers warned not all OE prepped glass was equal in terms of proper priming. OE’s make mistakes like everyone else. I’ve previously written about problems with priming that must be addressed if witnessed.

I urge all technicians and owners that read this article, to check with their adhesive representatives or check their adhesive instructions to verify the procedures in dealing with pre-primed OE parts. If your urethane of choice has neither a rep nor written instructions covering this issue, the only way you can be assured the primer on the OE part is compatible with the urethane used is to purchase the OE urethane kit with the OE glass part. Then follow the written instructions given to you by the OE adhesive company.