Many people doubt the value of a chip repair. Paying fifty bucks for a chip repair that is barely the size of a nickel seems unreasonable. However, most do not realize that the windshield is very fragile to internal stress. It may look impenetrable, but when subjected to road and temperature stress, the chip can easily become a crack. Searching recent forums, an Acura owner’s tolerance of “an annoying little rock chip [had] finally become a long streak across the middle of [his] windshield.” (1)
As with all things, let’s begin with the basics.
Windshield glass is a type of laminated glass. It consists of two layers of special composite glass with a laminate in between the layers. The laminate usually is made from a form of vinyl plastic, which is in simple terms, a very strong plastic. The laminate acts as a sticking board for the inner and outer layer of glass, which serves to hold both layers together and provides a surface in the event of shattering for glass fragments to adhere to.
A black frame, referred as the ‘frit’, lines the outer edges of the windshield, commonly 2-3 inches wide and even wider on top. The frit protects the urethane molding (generally speaking, glue that bonds windshield to car) of the windshield from the sun’s ultraviolet rays. Without the frit, the urethane would melt and cease to hold the windshield to the body frame. This is what happens with rear-view mirrors that are incorrectly installed; they fall off the windshield after the adhesives melt in the sun’s heat.
Functions of Your Windshield
Windshields play essential roles in vehicle safety and drivability. First and the most apparent function of the windshield is blocking wind and airborne debris from you and providing a clear perspective of road conditions. This is more of a drivability issue. The next two functions are safety-related, especially during an accident. In a frontal collision, two safety features of the car minimize impact damage to the driver and passenger: SRS Airbag and seat belts. In order for the airbag to deploy properly, the windshield needs to be in place. It stops the airbag from deploying upwards and redirects the direction of inflation toward the driver. In a rollover, windshield serves dually to prevent the roof of the car from collapsing and the passenger from having any body parts hanging outside the car. This issue is more pertinent with side windows, where loose body parts will dramatically increase fatality rates.
An improperly installed or cracked windshield will jeopardize your safety. One, the windshield may crack up and eventually lose integrity and shatter. Two, during an accident, the windshield will fly apart on airbag deployment with shards of glass spewing all over the place. And the airbag will be less effective. Third, on a rollover, compression stress will first stretch the crack from end to end and then finally break the windshield. Flying glass shards are very sharp and dangerous.
How Your Windshield is Installed
Ok, are you still following me? In the above sections, I have mentioned windshield structure and function. This section will cover windshield installation. The next section will tell you about windshield stress areas that dictate how likely a chip or crack is going to develop further.
Windshield placement is a highly robotic and computer-controlled process in the assembly line of automobile manufacturing. Computerized alignment and placement procedures ensure that both molding and windshield are accurately fitted. Preparation of the car frame provides a clean surface to which the windshield could bond. Furthermore, there is ample time between windshield installation and the end of the production line for the molding to cure. Because of these exacting processes, the quality that comes out the factory is the best.
For aftermarket windshield installation, getting rid of the original windshield properly is foremost to a good replacement. The correct installation techniques require removal of the old molding and lower windshield cowl panel. Subsequently the glass is cut out, leaving around 1/16″ of urethane bedding. The channel area, where the urethane adhesives bond, should be primed to inhibit rust formation. Rust formation will eventually weaken the bonding of the windshield to the car. After placement of the windshield, the car should be given from 1-24 hours to cure, depending on the adhesives used.
Some unethical replacement practices include shortcuts, such as close-cutting, flush-cutting and jumping-the-cowl. These will not be covered here, but if you are interested, you may read about these shortcuts in brief in the second link in References.