A short time back, Carolyn Rack of Beyond Parts and Equipment Magazine, (BP&E serves the automotive repair industry, with an emphasis on collision repair, including glass repair; 16,000 circulation, nationwide), called me and told me that someone she knows had removed a windshield from a vehicle and found a large amount of rust on the pinchweld of the windshield opening. Also noted: the windshield had been previously replaced by someone using the "close cut" or "shortcut" method. This was assumed to be the cause of the rust.

How, she asked, could the glass industry allow a practice that did such damage as to seriously compromise a windshield's ability to support the roof and retain the passenger-side air bag as the car manufacturer designed it to? After I'd explained, she said, sweetly, "That would make a terrific article! When can you have it ready?"

To keep this as short as possible, I'll generalize as much as possible from all sources as well as from my own views and practices. There's a wealth of information on the close cut vs. full cut methods of windshield replacement.

Definitions

Close cut, or short cut, means removing a windshield by cutting as close to the glass as possible, leaving the original bead of urethane in place. The installer then puts a new bead of urethane on top of the original, and installs the new glass.

Full cut means removing almost all the original bead of urethane after the glass is removed, cutting as close to the pinchweld as possible and leaving a very thin layer of the original bead intact. Then a very much larger bead of new urethane is applied, and the new glass installed. Most major car manufacturers support and endorse the full cut method; some flatly reject close cutting.

Essex, manufacturer of auto glass urethane adhesive and OEM supplier to all major car manufacturers, favors full cutting. In my experience, Essex's efforts to provide information for the glass replacement industry is second to none, and the vast majority of cars come from the factory with Essex urethane under the windshield.**

The Rust Problem

On all installations, it's critical to re-prime every scratch and every bare area of steel that results as installers remove a windshield and prepare the pinchweld for installation. Only re-priming can seal the body and provide the best possible surface for bonding again. Any exposed, unprimed area is a potential rust site. Unfortunately, many installers are too rushed to properly follow the strict guidelines required for close cutting.

In my experience, the most common cause of rust is running a utility knife around the perimeter of a windshield to ease the cutout knife's passage through the old urethane. This scores the metal all around the perimeter and leaves an entire circumference of potential rust problems. Using a utility knife is a terrible practice that saves only seconds on the removal.

It takes only a couple of minutes to re-prime an exposed surface, but, again, many installers don't take the time, just don't care, or weren't properly trained in the first place. Many installers who think they're doing proper close cut installations are actually doing "fast-track" or "quickie" installations, again due to lack of training or lack of caring.

Bottom line: rust is due to very poor workmanship, no matter what the installation method.

Full Cut Advantages

Varying Curvature

The full cut method is generally preferred for many reasons. First, the curvature of the replacement windshield may not be identical to that of the original. This may cause stress breakage. Full cutting, plus the larger bead of fresh urethane that full cutting allows, helps to assure a windshield's proper fit despite any differences.

"Decking"

Second, a "decking" problem may occur with close cutting. When you stack urethane on top of urethane, the glass inevitably sits "higher" off the pinchweld. This, too, can induce stress breakage due to the fact that many vehicles' doors now close tightly to the windshield moldings at the A-pillars.

Urethane Compatibility

Third, urethane compatibility requires never close cutting on top of a prior close cut. For the reasons above, yes, but also because you're combining potentially dissimilar urethanes with no crash test data to assure that you're returning a vehicle to its original crash worthiness.

There are many ways to scratch the pinchweld down to bare metal when removing a windshield; realistically, it's almost unavoidable, but re-priming restores the bonding surface and restores the rust protection that was provided by the manufacturer. It is one of the single most important aspects of glass installation for the body of the car and the glass.

Critical Data

Installers must know the precise installation procedures required by the urethane manufacturer whose product they're using, follow those guidelines to the letter, and document every installation with all aspects of the installation. These recorded facts, which should be saved for at least five years, are:

• All vehicle and owner data.

• Glass manufacturer.

• Urethane manufacturer.

• Lot numbers of urethane and primers.

• Shelf life of products.

• Pre- and post-work inspections.

• Proper urethane cure times.

• Customer acceptance and acknowledgment of all the above.

Cautions for Body Shops

If you allow outside vendors or installers to install windshields in your shop, insist that they give you this information. This will be your only protection when something happens. If work is done in your shop, you'll very likely be implicated in a lawsuit if a poor installation is ever determined to have caused injury.

Pay no mind to the fact that an insurance company may have sent the installer. You're the professional; you, not the insurer, are responsible to know what's best for people who have entrusted you with their car. If an installer won't give you this information, my humble advice is to find someone who will.

Watch the installation. Be sure the installer uses the products listed on the Service Record. It's fast becoming common knowledge lawyers are seeking victims ejected through windshield openings in collisions--glass that doesn't stay in the car in an accident. Multimillion dollar liability is nothing to take lightly.

Three minutes' documentation per job is worth lots to you and your customers.

Mark Rizzi owns ACR in Alliance, Nebraska; you may reach him at 308-762-3526
** For this reason I personally use only Essex Urethane.