Auto Glass Repair vs. Replacement
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Auto Glass Repair vs. Replacement

Glass chips and cracks are inevitable when you drive your car, whether you’re involved in an accident or just have gravel and other debris strike your vehicle. When this happens, is it better to repair the glass or have it repaired? The answer depends on a number of factors including the type of glass, the size of the damage and the location.

What Makes Auto Glass Different from Other Glass?

Auto glass does more than seal in the cabin and provide a clear view. It also has to withstand vibrations and impacts, act as a structural member and fail in a way that minimizes the chance of injury in an accident.

All windshields in cars built in the past 60 years and some rear windows in recent vehicles are made out of laminated glass. This glass is made by bonding two sheets of glass together with an inner layer of polyvinyl butyral (PVB) plastic. This plastic layer acts as a shock absorber so the glass can withstand vibrations and absorb debris impacts. It also has the side benefit of being UV reflective, protecting the interior from sun damage. If the glass cracks, the plastic keeps the pieces from separating and turning into projectiles. The windshield is an important structural component, providing 45% of the vehicle’s structural integrity in a front-end impact and 60% in a rollover.

Side windows and most rear windows are made out of tempered glass. This glass is heated then quenched with jets of air. This causes the center of the glass to cool faster than the outer edge, creating internal tension. This increases the glass’s strength, and if it breaks, the release of this tension will shatter the pane into small, rounded pieces.

How Does Glass Repair Work?

Cracks and chips in laminated glass can be filled in with a resin. To do this, dirt and loose glass are removed from the area to create an even surface, then a pressurized nozzle forces the resin into the crack to fill in the gaps. Like automotive paint, this plastic has to be blended and applied in different ways depending on the temperature and humidity. A UV light is applied to cure the resin, then the repaired area is polished until it’s even with the rest of the glass surface. Even the best repair can still leave a visible mark on the glass, so it’s not a perfect solution.

When Can Glass Be Replaced, and When Does It Need to Be Repaired?

Tempered glass must be replaced because damage interrupts the pane’s internal tension, but laminated glass repair also has its limits. According to the National Windshield Repair Association, these are the current limits for damage that can be repaired under ideal conditions with the best equipment on the market:

– A “bullseye” no larger than one inch – this crack has a separate cone of cracking on the outer glass pane
– A “star break” no larger than three inches – this crack has legs extending out from the impact
– Surface pits at least 1/8 inch in diameter
– Cracks no longer than 14 inches

In many cases, a crack or chip may not be repairable due to its placement:

– Cracks near or over the edge of the windshield compromise its strength, even after a repair.
– Any damage directly in the driver’s view can reduce visibility, even after a repair. In many cases, this type of obstruction will keep the car from passing a license inspection.
– Repaired damage can interfere with the view of sensors used for features like lane departure and automatic braking systems. These sensors are usually at the edge of the windshield, so a repair wouldn’t be possible anyway.
– If the resin from a previous repair separates from the windshield, it can’t be refilled.

Where Can I Go to Get My Glass Repaired or Replaced?

If you want the best chance of getting quality glass repair, bring your car to Merton Auto Body. Our I-CAR certified technicians use the latest techniques and equipment to prepare and fill in the glass so you’ll have a permanent repair with minimal flaws. Have damage that can’t be repaired? We can replace it. Our auto body estimating center can have an estimate ready for you in about 15 minutes, and our on-staff appraiser can work with your insurance company directly to get work approved so you’ll be back on the road in no time. Visit our website to schedule a free online estimate or stop in at our Sussex, WI location. We proudly service the Waukesha County and surrounding Lake Country areas, including Oconomowoc, Delafield, Hartland, and Pewaukee.


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