A big block of masonry fell on your parked car and now you’ve got a gaping hole in your windshield. (Groan!) Better go shopping for a replacement. Or a bit of flying debris smacked into your windshield when you were “doing 100” on the highway and now it has a small crack. (Sigh!) Better repair it before it lengthens. What, though, if your windshield has a chip two inches across? Or if it has a ten-inch crack?
Windshields are specially designed to provide structural support for the vehicle as well as to stand up to the stress of traveling on highways, but damage does inevitably occur. Windshields are actually made up of two layers of glass which sandwich an inner layer of automotive safety glass. This inner layer, called the lamination, serves to hold together the broken outer layers in the event of an accident. This is why windshields crack when struck by objects, yet do not fall apart and cave in upon the driver in most everyday circumstances.
Repair or Replace?
In general, most chips and cracks can be repaired, but it always depends upon four factors: the size, type, depth, and location of the damage. Results will vary based on age, amount of contamination, location & the severity of the damage.
A qualified auto glass repair technician must evaluate a number of factors before deciding whether your windshield is repairable. Each case is assessed on an individual basis, and a determination is made based on the technician’s own skill with equipment, the expectations of the customer, and the probability of a high-quality repair. Some chips and cracks can be easily repaired without expensive professional help – see my guide on DIY crack repair and the best repair kits for all kinds of windshield damanges.
Size and Depth
Pretty much any shop should be able to repair chips of about one-inch diameter and cracks about three inches long. Traditionally, any crack larger than a dollar bill could not be repaired, so size was a very important factor in making the determination.
Rock chips can be repairable using a windshield repair kit if the diameter of the chip is less than an inch. But if the chip diameter is bigger and more than one inch in diameter, an auto glass replacement is deemed necessary.
However, new technologies are making it possible to repair wider chips and longer cracks, and to assess the odds of each individual repair being made successfully you should check with a technician – all cases are determined on an individual basis. These days, auto glass repair shops can easily fix cracks up to 18 inches long.
There are many different types of cracks, some can be repaired easier than others. For example, Star Break (short radial cracks coming off of the impact point), Bulls-Eye (circular damaged caused by circular object) or Partial Bulls-Eye (aka Half Moon, also caused by circular object, damage is not completely circular), Crack Chip (single crack size of a quarter), Ding (same as Crack Chip), or Pit (small piece of glass missing) can be easily repaired.
In general, chips and cracks that can be covered with a quarter can usually be repaired because glass shops center equipment over the break.
Multiple cracks are more difficult to repair, so if you don’t have a single crack you need to check with technician whether it can be repaired.
Even good repairs may leave behind some discoloration, mistiness or unevenness, and if the damage is in the driver’s line of sight, the repair would decrease clarity and reduce visibility. The technician must consider all potential drivers of the vehicle when determining the line of sight over the steering wheel because this can vary depending upon the height of each driver.
Any crack that is at or very near the windshield’s edge, or any chip at or near the edge that has caused the windshield to start cracking, attenuates the strength and integrity of the windshield and its bonding to the surrounding metal frame, which in turn compromises passenger safety.
If the technician cannot fully see the crack or chip, then he may not be able to successfully repair it.
Damages that usually cannot be repaired:
- on inside of the windshield
- deep damage on both layers of glass
- damage over rain sensor, internal radio antenna
- damages that reach into the driver’s critical viewing area
- complex multiple cracks
- very long cracks (i.e. over 18 inches long)
- contaminated cracks
- edge cracks and chips
Now if you have a couple of chips near the top, passenger-side corner, you might think, “May as well get a replacement, given the repair cost and my low deductible.” But you may end up paying nothing for the repairs! The fact is that the vagaries of auto insurance will also influence your decision.
In any event, as soon as you notice a chip or crack on your windshield, ‘speed’ is of the essence. Quite often cracks lengthen before you know it. Also, cracks can radiate from chips. Furthermore, dust accumulates inside chips which can cause further damage and makes repairs difficult. As such any delay could result in what would have been an inexpensive repair job to turn into an expensive replacement.
Repairing one chip or repairing one crack typically takes about 30 minutes, sometimes 40 or more, occasionally less. If the chip or crack is deep or dust has accumulated into it, preliminary steps are necessary. Windshield repair involves injecting a clear, curable resin into the outer layer of glass in order to restore its integrity and improve the appearance of the glass. The resin is then cured and polished, leaving a smooth surface, and the crack or chip is unable to spread and cause further damage. A qualified auto glass repair technician must evaluate a number of factors before deciding whether to repair the glass or replace the entire windshield.
A deep or slanted crack or chip may have damaged the intermediate Poly-Vinyl Butyral (PVB) layer. In such a case the crack or chip is slightly enlarged or deepened with a drill to make the hole smoother and more even so that in the subsequent step resin can reach the intermediate PVB layer. Any dust or debris in a chip needs to be thoroughly removed first; this is usually done with a small vacuum.
For repairs, an ‘injector’ is attached to the windshield around the damaged area and a small quantity of a special resin is injected into the chip or into and along the crack. The excess is removed after which UV light is applied for curing and hardening the resin.
A chip that is bigger than two inches across or a crack one foot or longer will (almost surely) require your windshield to be replaced – tough luck! You have a choice between going with a ‘Same-OEM’ windshield, an ‘OEM-Aftermarket’ substitute, or a ‘Third-Party Aftermarket’ alternative.
In the United States, the Auto Glass Safety Council (formerly AGRSS) certifies technicians and registers glass shops that meet their standards, thereby quasi-regulating windshield replacement. They maintain www.safewindshields.org where they list approved glass shops.
Windshield replacement is a four-step process. First, the areas of the car body around the windshield and the nearby interior are protected with canvas or such. The windshield is then cut from the edges and removed, as are the seals and glues, leaving behind the bare frame. Next, a primer is spread on the inside of the frame where the windshield will be fitted after which the new windshield’s edges are coated with a special adhesive sealer with a polyurethane base. A very short time is allowed to elapse before the windshield is carefully fitted and bonded to the frame.
This replacement process usually takes from half-an-hour to 60 minutes.
But wait— before you start doing 60 miles, most repair shops ask that you wait a further 60 minutes to allow the adhesive to set and bond. So if you have the windshield technicians do the replacement at home, well and good, but if you go to the auto glass shop, take a book!
There is a Right and Wrong Ways to Replace a Windshield, so even when you go to a repair shop, make sure you do some due diligence and make sure that standards are followed. To keep your windshield in a good health, make sure you know how and when to clean it.