Winter Weather and Rock Chip Repair


Glass will always behave in several predictable ways. Your windshield is no different inasmuch as you can pretty much predict what will happen under certain circumstances. Cold weather causes the glass to contract and the variance between the temperatures
on the inside layer of the windshield versus the temperature on the outside, can easily cause the windshield to crack.

  • Glass expands in the heat and contracts in the cold
  • The size of the rock chip does not determine how stable the damaged area is.
  • Left un-repaired, it is not a question of whether the damage will expand, it is a question of when.
  1. If you’v ever experienced accidentally breaking a glass when you held it under water whose temperature was either too hot or too cold, you already know that if you hold a hot glass under cold water, or visa versa, it is going to break. This is because the variation in temperature causes the glass to either expand or contract, and to relieve the pressure, the glass cracks. This is exactly what happens to your windshield. When your windshield is damaged from a rock, it is already unstable. If you run your car heater in the colder weather, or if you run your car air condition in the warmer weather, you are setting up the same conditions as running a glass under water of the opposite temperature. To relieve the pressure, your windshield will crack, resulting in the need for a costly replacement.
  2. The size of the rock chip has little to do with whether the damage will spread. Drivers are lulled into thinking that because the damage is small, it is unlikely to grow in size. This couldn’t be more wrong. I can’t tell you the number of times a customer’s story starts out with, “it was such a small, little rock chip, and then suddenly, without any warning, we came out to the car to find it had grown into a 9″ crack.” The windshield is unaware of the size of the damage. The laws of physics are all that applies here. It is simply this: Damage of any size, will eventually grow and spread to the place on your windshield with the least amount of pressure. You can count on it.
  3. Most drivers think that because a rock chip that occurred months, or even years ago, has not spread, that it will never cause a problem. Again, this couldn’t be more wrong. If you don’t treat the rock chip, regardless of how long you’ve gotten away with it not spreading, it eventually will grow in size. it isn’t a question of “if” it is a question of, “when.”

Small Rock Chip – Big Problem!



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.

  1. 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.
  2. 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.
  3. 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.
  4. 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.

Rock Chip Repair & What To Expect

The windshield repair technician’s primary goal is to keep the damage from cracking further, resulting in the need for a more costly windshield replacement. A quality repair performed by an experienced technician should leave the windshield 100% structurally restored to pre-damaged condition. The cosmetic result, however, will depend on a multitude of factors.

imgres-11. The extent of the damage.

Typically, but not always, the more extensive the damage, the more visible the result will be. While glass can be repaired 100% structurally, it will usually repair 75-80% cosmetically. Fractured glass, even when repaired, will no longer refract light the way it did before it was damaged. Also, when the rock hits, it shatters the surface glass and propels it inward. This too, can lead to a more visible repair.

2. The length of time the damage has been there.

A rock chip treated soon after it occurs will almost always look much better than one that has been there for months or even years. The impact of a rock or debris that has caused windshield damage, leaves an open hole into the windshield. This entry point allows dirt, debris, and moisture to accumulate over time, and it is very difficult, sometimes impossible, to remove. I often advise customers to cover the rock chip with a piece of clear packing tape (the kind used to ship a package) immediately after the rock chip occurs. This helps to effectively keep anything from getting into the damaged area.

3. Miscellaneous Circumstances.

Often vehicle owners will try to treat rock chips with “home remedies” and do-it-yourself kits. Common home remedies include: Crazy Glue, clear nail polish, and Gorilla Glue. None of them work, and most often they ruin the windshield. The technician can’t get the glue out of the rock chip and so there is no way to complete the repair process. I call do-it-yourself kits, “one shots.” On a very superficial rock chip with no complications, the home repair kits will sometimes take care of it. You only get one chance (“one shot”) though with a do-it-yourself kit. If it works on the first try, you have lucked out. Most often, however, a rock chip repair requires several fill and vacuum cycles. Resin is injected and then air, dirt and debris is removed, and then another pressure cycle to add more resin, etc. Sometimes this procedure is repeated three or even four times before the repair is completed. Only professional windshield repair tools will allow for this. Windshield repair is not one of those things you can “just do.” You have to know what you are doing or you risk irreparable damage.

Often customers show up thinking that their primary goal is to save their windshield, and the secondary goal is how the windshield will look once it is repaired. After the repair, we often find that the cosmetic result was actually more important to the customer than saving the windshield was.

In short, what can you expect from a windshield repair? A technician should only accept the job if they feel the repair can be completed successfully. This means that the technician has determined that the result will leave the windshield 100% structurally restored. The customer should expect that small, superficial damage will appear approximately 75-80% better cosmetically once it has been repaired. That’s it. While larger, more extensive damage sometimes falls into that 75-80% range, there is no guarantee that it will. If the visible, cosmetic result of more extensive damage is not something you are prepared to live with, you are not a candidate for a windshield repair, You are more likely looking for a windshield replacement.

Hot Weather & Windshield Repair



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:

  1. 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.
  2. 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.
  3. 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.

What Will Work & What Will Not.


Its tempting to try to repair a rock chip on your own. After all, how hard could it be, just to fill a silly little hole in your windshield? The answer is, very hard!

Here’s what won’t work:

  1. Crazy Glue. At first, Crazy Glue seems like a perfectly good choice to fill a rock chip. Here’s the problem. To begin with, it will not stand up to the elements. Super Glue is not meant to withstand extreme heat, cold, rain, snow, etc. It won’t take long before it starts to peel away. Unfortunately, some of the glue penetrate the top layer of the windshield through the open whole that the rock chip created. Once it gets in and hardens, there is no way for a windshield repair technician to fix it. In other words, you are screwed, to put it bluntly.
  2. Clear Nail Polish. Much like super glue, nail polish will just gum up the works and make it impossible for a technician to “re”repair the damage.
  3. Gorilla Glue. Really?
  4. Any other foreign solution or epoxy.
  5. Do-it-yourself Kits. If any repair solution other than using a qualified technician has the chance to work, it is this one. However, repairing a windshield requires that the acrylic resin used in the process remains fluid long enough to allow it to fill the entire rock chip, without hardening (curing). As soon as acrylic resin is exposed to UV light, which is present even when there is no sunlight, it starts to harden. You get one shot with a do-it-yourself kit. If the desired result is not achieved in that one shot, its over. You will have to live with what ever the result.

Here’s what will work:

Have your windshield repaired by an experienced, professional -plain and simple.


Warm Weather & Rock Chip Repair


Now that Spring is here and the weather is getting warmer, here are some tips on how to keep rock chips from spreading, and how to prepare for your windshield repair.


Glass expands with heat and contracts in cold temperatures. Your windshield has three layers. The inside and outside layers are made of UV glass. The middle layer is a synthetic called polybuterol. The three layers are laminated together to form a strong bond. Each layer of the windshield, especially the outside layer and the one inside the vehicle, expand and contract at different rates. Ordinarily this variance does not present a problem. However, when the outside layer is damaged, the variance can cause the rock chip to crack as it attempts to relieve the pressure that is building up. Other factors can also exacerbate the problem. For example, if your windshield is very hot and you run your air conditioner, you may set up a similar circumstance as running a hot glass under cold water. It will most likely shatter. If the temperature of your windshield is very cold and you run your car heater, you may set up the same circumstance, only in reverse.

Here’s how you can help to stabilize the damage and what do do before you arrive to have it repaired.

  1. Cover the rock chip with a small piece of clear packing tape, right after the rock chip occurs. This will help to keep dirt, debris and moisture out of the damaged area and it will help to stabilize the damage.
  2. Avoid extreme temperature fluctuations. Don’t allow the windshield to get too warm by parking in direct sunlight. Even when the temperature outside is 60 degrees, parking in direct sunlight will heat the windshield to well over 100 degrees.
  3. Your windshield has to be cool to the touch in order to attempt a windshield repair. Remember, glass expands in the heat. The repair process uses some pressure and it can cause the damage to crack if the windshield is too hot. We will not attempt to repair your windshield if it is too hot, so to avoid wasting time, make sure that when you arrive it is cool enough to work on. To do so, run your car air conditioner on low, on the way to your appointment to have your windshield repaired. This will cool it down adequately enough to work on.


images.jpgI’ve written before about the average cost for a rock chip repair, but it is worth going over again. Taking in to account that the cost of living varies in different parts of the country, the average cost of a rock chip repair ranges between $50-$75.

-That being said-

Almost ALL AUTO INSURANCE COMPANIES will cover the cost of windshield repair, regardless of your deductible, and with no negative effect on your premium. Here is why they do it. Many people carry very low deductibles, sometimes as low as a zero, $50, $100. Insurance companies want to cut down on the number of drivers opting to replace their windshields when they have a rock chip. Replacements cost the insurance companies a small fortune. It is in the interest of the insurance company to pay for your windshield repair, hoping to cut down on the overall number of replacement claims. On first glance it appears that the insurance company is doing you a favor by covering the cost of windshield repair, but in fact, it is you doing the insurance company the favor by agreeing to have your windshield repaired and not replaced.

There are only a handful of insurance companies that do not cover the cost of windshield repair, so it is a good bet that you are covered. If so, it is a simple claim to file and the insurance company pays us directly, so there is no cost to you for the repair.

In Northern California, where we have our shop, the only two insurance companies that do not cover the cost of windshield repair are:

  1. State Farm
  2. Mercury Auto Insurance.

When you are ready to schedule an appointment for your repair, contact us and let us know which auto insurance you carry so we can tell you if you are covered. We’ll also help you with filing the claim.

American Glass Repair