Often drivers are lulled into a false sense of security by a small rock chip. They imagine that a small rock chip is somehow less likely to grow in to the dreaded crack that makes its way all the way across the windshield if left untreated. To begin with, most cracked windshields start with a small rock chip which later expands into a long crack. The crack may spread immediately, over night, or even in a matter of months to years. There is simply no way to tell when the damage is going to spread. Often customers inform me that the rock chip I am about to repair has been there for several years. I always tell them the same thing, which is that they have been on borrowed time, and very lucky at that. A rock chip may seem stable for a long time and then circumstances align causing it to suddenly break. Here’s some of the factors and physics behind what causes a rock chip to spread.
Glass tends to expand and contract in the heat and the cold. Usually, the rock chip you can see with your eyes also contains several invisible micro cracks which extend further out. When the glass expands in the heat or contracts in the cold, already weakened by the impact of the rock, it may give way, cracking sometimes up to 2 feet or more.
The impact of the rock hitting the windshield has removed a small piece of the surface glass, weakening the structural integrity of the windshield. Vibrations and bumps in the road can easily cause the chip to crack.
Differences in atmospheric pressure can also cause a weakened windshield to crack. Often drivers report that a rock chip that had been on the windshield for months, suddenly cracked when they went into the mountains.
Last, running the car heater or air conditioning can cause an unstable rock chip to crack. Like running a cold glass under hot water, or hot glass under cold water, the difference between the temperatures of the outer and inner layers of the windshield can cause the glass to shatter.
The size of the rock chip is immaterial. A tiny rock chip is just as likely to crack as a larger one. The same physics behind large rock chips are in play with smaller ones. That’s why I say that drivers are often lulled into a false sense of security when they have a small rock chip. I can’t count how many times I’ve heard the same story. It always starts something like this: “I had this little rock chip on my windshield that happened a few months ago and I thought, it was no big deal. Then I came out yesterday and it had spread to over a foot long. Is there anything you can do?” And of course, the answer is, “no”.
Rock chips are a pain in the neck no matter what size. My advice is to have it repaired immediately so it doesn’t become a much bigger, much more expensive, pain in the neck.
Glass will always behave in a relatively predictable way. There are a few “enemies” of windshield repair. Extreme temperatures is one of them. Glass tends to expand in the heat and contract in the cold. The windshield is comprised of three layers, UV glass on the outside, UV glass in the interior of the car and a synthetic in the middle, laminated together to create a strong bond. When it is very hot outside, especially when the car has been sitting in direct sun, the windshield can heat up to well over 110 degrees F. More than likely, drivers will run their car air conditioner on a hot day and if there is a rock chip or a small crack on the windshield, the variance in the temperatures from the outside of the windshield and inside the car, can easily cause the damage to grow in size resulting in the need for a costly windshield replacement. Here’s why: The outer layer of glass is expanding in the heat. The middle layer is fixed, and the inside layer is contracting from the cold air blowing from the air conditioner. This causes a certain amount of pressure, and to relieve the tension, the glass cracks. It is the same principle that cause a hot glass to shatter if it is held under cold water or visa versa. In the Winter, the same thing can happen, only in reverse. The outer layer of the windshield is icy cold and when the car heater is turned up, the inside layer begins expanding with the heat.
The take away from this, aside from having your windshield repaired asap when you have a rock chip, is:
Avoid extremes in temperature. If you are still using the vehicle before you have a chance to have it repaired, try to park it in a shaded area, out of direct sunlight.
Avoid using sun reflectors that are shiny. Shiny reflectors will shield the interior of the car by reflecting sunlight away, but they are also known to heat the windshield to temperatures that can easily cause a small rock chip to spread. Instead, use opaque, or satin-finished sun guards.
If you are using your air conditioner, keep it on low, and keep the setting adjusted so that the air flow is focused mainly on your legs and not on the windshield.
-Simple tips that can help to save your windshield.
I see this all the time. Some one shows up at my garage for a windshield repair and within 5 seconds, I can tell that they’ve attempted to repair a rock chip by using Krazy Glue, Gorilla Glue, clear nail polish – you name it – whatever else they think makes sense at the moment. The trouble is, nothing will work except acrylic resin, properly used by a professional. I’ll ask, (already knowing the answer), “Have you used any type of product on the rock chip trying to repair it yourself?” Almost always the customer tells me no. I don’t press the issue, even though I can clearly see that something was used on the damaged area. At that point, the customer really needs a rescue and not a repair. Unfortunately, once a product like Krazy Glue has been used on a rock chip, there is no way to repair it properly. The glue gets into the rock chip and hardens, preventing the acrylic resin from doing its job. Only acrylic resin can be used to repair windshield damage. Anything else will ruin the windshield and eventually result in the need for a costly replacement. Krazy glue may support the weight of a grown man, as seen in the photo, but using it on a windshield is one quick way to end up in a glass replacement shop.
Great! – You’ve made an appointment to have your windshield repaired. That’s a good first step and could very well be just what you needed to do, to save your windshield from cracking further. Here’s a few tips that will ensure the best possible result.
Your windshield has to be cool when being repaired in order to minimize the risk of the damage cracking further. Auto windshields are comprised of three layers which are laminated together. The windshield is both strong, and somewhat flexible. As with any glass, it expands in the heat and contracts in the cold. If a technician attempts to work on the glass when it is too hot, or too cold, it can easily crack. Ideally the windshield should be between 60 – 80 degrees, but around 70 degrees is optimum. When scheduling your repair, if it is very warm outside, try to schedule an early morning appointment before the temperature rises.
At least an hour before the repair, keep the vehicle either in the garage or in a shaded area. Even when the temperature outside is only 70 degrees, the windshield will heat up to well over 100 degrees if it is in direct sunlight.
If it is warm outside, turn your car air conditioner on medium to high and defrost while you are driving to your repair appointment. This should cool it down by the time you arrive so that it is ready to be worked on.
If the temperature outside is cold, use your car’s heater on defrost to warm the windshield. You do not want to heat the windshield so that it is above 60-70 degrees. Remember what happens when you run a cold glass under hot water or visa versa? The variance in the temperature will cause the glass the break.
If water is present in the damaged area, the result will be less clear than if no water is present. Immediately after a rock hits, cover the rock chip with a clear piece of packing tape, (the kind you use to ship a package). This will help keep out dirt, debris and most importantly, moisture.
This morning, a customer showed up and I could see that there was something in the damaged area that appeared like glue. I asked the woman if she had attempted to repair the damage on her own or elsewhere and she told me that her husband bought a do-it-yourself repair kit, attempting to repair the damage himself. The do-it-yourself kits rarely work as advertised. This woman was driving an expensive BMW and her husband’s attempt to repair the damage left the windshield in pretty bad shape. I did my best to fix what he had repaired, but the result was very visible. I saved the windshield from cracking further, but she will have to live with a very visible, permanent “scar.” Never attempt to repair a windshield on your own. I’m not advising so because I want the business, (which I do) but because a windshield is a far more complicated system than one might imagine and like any essential component of your vehicle, it needs to be repaired by a professional.
As the weather begins to cool around the country rock chips that have been unattended to become particularly vulnerable. The short and simple of it is that glass tends to expand and contract based on ambient temperature. If there is a rock chip which has not been repaired, your windshield has already been weakened, even if it appears to be stable and even if the rock chip has been there for ages. The physics involved is also simple. The small micro crack caused by the rock chip will do its best to find a path of least resistance to the furthest point on the windshield to relieve pressure. This is why a spreading crack often appears more like artwork as it swirls around the windshield searching for a final resting place -which usually ends up in an auto glass replacement shop!
All of this is actually avoidable most of the time. While the laws of physics will eventually hold up, all you need to do is have the rock chip repaired before physics makes the choice for you.
Let’s face it, the cost of having to repair or replace your car windshield is about the last expense you were planning for. Unfortunately, there’s no predicting when that gravel truck you are riding behind or the uncovered lawn care truck in the next lane, is going to kick up a rock or some other debris. You hear the unmistakable sound of one of these little missiles as it rockets towards your windshield. You know it hit, but at first you can’t see any damage. You breath a sigh in relief only to discover sometime later, the tell tale star break or bulls eye you thought you had escaped. Here’s a guideline and some advice when deciding whether to have your windshield repaired or replaced.
Windshields, unlike most other parts of your vehicle, can not be recycled. The PVB layer laminated between the outside and inside layers of UV glass is a synthetic, resembling a soft plastic. For some, this alone is enough to make them opt for a windshield repair when at all possible.
The repair process works best on rock chips about the size of a quarter or less. Damage larger than the size of a quarter can still be repaired, but typically, the greater the damage, the more visible the result will be. Some glass technicians and shops will repair cracks greater than 12 inches in length. In theory, any length crack can be repaired but it is not wise to do so. A repaired crack will be quite noticeable and more importantly, it will refract light differently from that of a non damaged windshield. This can cause the driver to be distracted and potentially lead to an accident. If a traffic officer spots a noticeable crack on your windshield you will get a ticket even if the crack has been repaired. Insurance companies often use a 6″ or dollar bill rule when approving or declining a repair claim. They will ask you if the repair is smaller than a dollar, and if so they will approve the claim. My own shop does not do crack repair and we typically only repair rock chips which are about the size of a quarter or less. We do this because we can control the quality of the repair. Customers are most often satisfied and insurance companies always approve our claims.
Repair windshield damage up to about the size of a quarter.
If you do decide to have a longer crack repaired, make sure the crack is less than the size of a dollar bill and not in the driver’s line of sight.
Not all glass shops are the same. You owe it to yourself to do the research to find a glass shop that meets high standards. To begin with, when filing a glass repair claim with your insurance company, ask them to refer you to a “tier one” shop. Here’s why that makes a difference. With exception of a few, most insurance companies use glass networks who contract glass repair shops and technicians to do their glass repairs. In fact, most often once you tell the initial representative at the insurance company that you are filing a glass repair claim the next person you are transferred to is not even an employee of your insurance company, they work for the glass repair/replacement network. The network has contracts with hundreds of glass shops and technicians, all who have varied levels of expertise and experience. The networks need to match up your claim with a technician in your area based on your zip code. This is where requesting a tier one shop / technician makes a difference. Often, tier one service providers are rightfully busy, because they are in demand. If the network can not find a tier one shop to do your repair they move down the list until often your repair is being handled by someone with little to no experience at all. Ask yourself one question: do you want your windshield repaired by a glass technician with little to no experience? The answer is obvious, no.
Search out reviews on Yelp where you will see what others are saying about a shop the network has recommended. if the reviews are not primarily 4 and 5 stars let the network know you prefer another shop. By law, you have the right to choose whichever glass shop you want to use to do the repair. Networks will often engage in an illegal practice known as “steering” where they funnel business primarily to their own shops and technicians that are in fact working directly for them. It is important to use a shop that is independent of the network so you know the only criteria used for the referral is the work the shop does and not any financial arrangement the shop has with the network.
Windshield repair is a one shot deal. By that I mean that once a rock chip or a crack has been repaired, there is no do-over. A bad repair, can not be re-repaired to make it better. Getting it right the first time is essential. To do this, you need to have a professional technician with a proven track record do the repair.