Car Windshield Stress Cracks

Do you take your car’s windshield for granted? Most of us do. After all, they quietly do their job with minimal fuss. Most drivers don’t give their windshields a second thought until a crack appears. When that happens, you begin to realize that this vital automotive component is fragile. It is made from glass – and glass breaks. While it’s understandable that a windshield might crack when struck by a rock, flying debris, or some other impact, some cracks, known as stress cracks, suddenly appear for no apparent reason. What are they? How do they form? And can they be repaired?

What are Windshield Stress Cracks? 

Car windshield stress cracks are cracks that appear in windshields for no readily apparent reason. How to identify a stress fracture in windshield? The rule of thumb is this: If there is no point of impact, it’s a stress crack. Though mysterious, windshield stress cracks usually have an underlying cause. Below are a few of the more common causes of stress cracks in car windshields:

Temperature changes – One of the most common causes of stress cracks is due to extreme changes in temperature. For example, if it’s an extremely hot day, washing the car with cold water could trigger a stress crack. The same is true of using hot water to melt an icy windshield.

Pressure changes – Pressure changes, including wind pressure, can also cause stress cracks. For example, explosions send out shockwaves which rapidly change the atmospheric pressure in a large radius from the blast zone. Cars located many miles away from the explosion can have blown out windows or cracked windshields.

Structural weakness / defects – Windshields play a vital role in the car’s safety systems. One of those roles is to support the roof in the case of a rollover accident. Another is to deflect passenger side airbags upon deployment. As such, windshields are installed with a strong adhesive. Uneven pressure can cause stress cracks. Manufacturing defects can also contribute. For example, when glass is annealed (heated and then cooled) during the manufacturing process, “residual stresses” are often found along the perimeter of the windshield. As a result, the edges of the windshield are also the weakest and most prone to fractures.

Repairing Windshield Stress Cracks

Stress cracks typically start from the edge of the windshield, and they can quickly become quite large. These two factors combine, making most stress cracks irreparable. In general, if a windshield crack emanates from the edge of the windshield (as is common with stress cracks), is in the driver’s line of vision, exceeds a certain length, or is contaminated with debris, the crack is not a candidate for repair.

The windshield repair process involves drilling into a crack and filling it with a resin that hardens within the crack. The goal is to stabilize the crack and prevent it from spreading. This is similar to having a dentist fill a cavity in your tooth. However, even if a crack is not in the driver’s line of vision, if it’s near the edge of the glass, it may not be repairable because suction device used to repair cracks needs sufficient space and a good seal.

If your windshield has small cracks that appear to be good candidates for repair, taking a “repair first” approach is worth considering. If the repair takes, you’ll avoid having to replace the windshield. If not, most reputable windshield replacement companies will apply the cost of the crack repair to a replacement windshield. Read about other types of cracks. If your stress crack cannot be repaired, please see “how much does it cost to replace a windshield“?

How much does it cost to repair a stress crack in a windshield

The cost of repairing a stress crack is the same as the cost of repairing other types of cracks. Usually you will be looking at about sixty dollars for the first one, and ten to fifteen dollars for any additional cracks. The cost of repair often depends on the type of auto insurance you have. If you have comprehensive, the repair often will be free.  Read more about cost and process or repairing cracks.

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