Auto glass isn’t something you really think about until it needs to be fixed, but at some point a hail storm, a gravel truck, or a car accident is going to do some damage to your vehicle’s windows. Why can some glass be repaired, while other glass needs to be replaced? What makes auto glass different from any other glass? How do you even repair glass? To better understand repairs, it helps to know what auto glass is, and how it can be fixed.
What’s So Special About Auto Glass?
Unlike architectural glass, automotive glass has to be able withstand constant vibration and high speed impacts. It also has to fail in a way that is as safe as possible since it’s right next to the car’s passengers. To meet these requirements, two types of glass are used: tempered and laminated.
Tempered glass is made by taking a normal piece of finished glass and repeatedly heating almost to its melting point, around 1,150°F (620°C,) then “quenching” it with jets of cold air. This cycle of rapid heating and cooling results in faster cooling near the edges of the pane. As a result, the center of the glass pulls away from the edges, creating tension. This gives it up to four times as much strength as untempered glass. How? Think of it like a rubber band: if it’s loose, it’s easy to flex, but if you pull the band tight, it becomes almost rigid.
When tempered glass does break, the tension is released, causing rapid cracking that leaves behind small pieces. This type of glass is commonly used in places where shards can be a serious safety hazard, like shower doors, refrigerator shelves and some smartphone screens.
Laminated glass sandwiches a piece of polyvinyl butyral (PVB) plastic between two pieces of glass. The layers are bonded together using a combination of pressure and heat, creating a uniform structure. When in use, the PVB acts as a shock absorber, giving the glass the flexibility to resist impacts. When it does fail, the cracked glass stays attached to the plastic so there aren’t any loose shards that can become a hazard. PVB also deflects UV light, protecting the interior from sun damage.
The safety factor added by glass goes well beyond visibility: the windshield makes up at least 45% of your vehicle’s structural integrity in a front-end collision and at least 60% in rollover accidents.
Since WWII, laminated glass has been used in windshields in all vehicles and occasionally has been used in back windows. All other automotive windows are made out of tempered glass.
How Does Glass Repair Work?
To repair glass, the hole or crack is filled in using a clear resin. This resin fuses the glass back together and absorbs vibrations, preventing further cracking. Or at least it will if it’s applied correctly, by a certified technician. While there are kits available for amateurs to repair glass, there are a lot of factors that have to be taken into consideration to make a lasting repair. That includes the size and shape of the damage, the current temperature and humidity, and the final finish left after the resin has been polished down to form a smooth layer. This is one place where it really requires professional level skill to get a good glass repair.
When can Glass Be Repaired, and When Does It Need to be Replaced?
With tempered glass, the need for a new piece is obvious: once enough of the surface has been disrupted, the entire pane will shatter. Even if it stays intact after a light chip, it’s still only a few movements away from failure.
Repair resin has its limits. It can’t provide the strength and abrasion resistance to fill in the edge of a pane of glass, and if the resin from a repair separates itself from the window, the hole left over can’t be refilled.
Put it all together, and repairs can only be made to minor damage away from edges and only on laminated glass. However, since this is by far the most common type of glass damage on cars, it means your car’s next encounter with a rock or a hailstone is probably repairable if it’s caught before the damage spreads.
If your vehicle’s glass needs repair or a replacement and you’re near the Waukesha County area, be sure to visit Merton Auto Body for a free estimate. You can visit them in person at W275 N6683 Moraine Dr. in Merton, WI or call them at (262) 538-1319 to schedule an appointment.