Windshield Safety

The windshield is an essential part of the safety net designed into the modern automobile by its manufacturer. Damaged windshields can compromise that safety net. Windshield repair is an internationally accepted procedure to restore the structural integrity and thus the safety of damaged windshields. However, all windshield repairs are not equal. This paper was prepared to assist the insurance company and its agents understand windshield repair and to provide sensible criteria for selecting a responsible, professionally competent windshield repair vendor.

Windshields are made of laminated safety glass. Laminated refers to the layer of PVB (polyvinyl butyral) sandwiched between two layers of glass during the manufacturing process. The glass and PVB become a single glass unit following the application of pressure and heat during manufacturing.

Safety is a primary function of the windshield. Protecting vehicle occupants from flying objects and road debris is just the beginning. In a crash, broken windshield glass adheres to the PVB layer rather than flying around the passenger compartment. The PVB layer also acts as a safety net to keep passengers inside the vehicle where they are less likely to be injured during crash situations.

Tips To Better Serve Policyholders

Time is important. Whenever possible, the insurance company should encourage policyholders to repair windshields right away. Windshield damage spreads rapidly. Temperature changes or even the natural flexing of the vehicle body can quickly turn minor, repairable damage into damage so extensive that only an expensive replacement windshield will suffice.

Satisfaction with the repair service is important to the insurance agent's continuing relationship with the policyholder. Always insist on an unconditional money back guarantee from a vendor; a credit toward replacement is not a proper guarantee.

Cost of insurance is a factor in selecting an insurance company for most consumers. The average windshield replacement costs over $250 today; the average repair around $50. By demanding windshield repair first, insurance companies reduce auto glass program claim costs and remain highly competitive. Many proactive insurance companies educate policyholders on the safety and economy of windshield repair prior to the existence of a need. Policyholders are then more receptive to repair over replacement, and, enjoy greater appreciation of their agent's efforts to control costs. Windshield repair can be a positive public relations tool.

Basic Windshield Repair Facts

Breaks in windshields occur when stones, road debris, or sharp objects impact the glass surface and physically dislodge pieces of glass. The break permits air to infiltrate the glass. The different refractive indexes of air and glass allow the human eye to see the damage. The same effect may cause vision distortions.

Repair replaces air in the damaged glass with a liquid resin. The resin is injected using vacuum and pressure where it is cured, or hardened, by exposure to ultraviolet light. The cured resin is optically matched to a refractive index of 1.51 matching that of glass to minimize distortion. When fully cured, the repair should restore the windshield to a tensile strength of 6,000 to 10,000 pounds per square inch. If this tensile strength is not achieved, you do not have an acceptable repair.

Size of the break is rarely a determining factor in selecting windshield repair. If in doubt, consult a qualified repair technician.

Objectives of windshield repair are:

Stop windshield dings or cracks from spreading. Restore structural strength to the glass.
  1. Improve optical quality in the damaged area.
  2. Smooth windshield surface for better wiper performance.
  3. Satisfy state safety inspection criteria.
  4. Prevent moisture infiltration into the PVB inner layer.
  5. Reduce fossil fuels wasted on unnecessary replacement windshields.
  6. Recycle damaged windshields otherwise headed for landfills.
  7. Keep insurance company auto glass claims low
  8. Save up to 75% of the cost of windshield replacement

Quality windshield repairs exhibit the following characteristics:

  1. Damaged area is clear and difficult to locate - 85% cosmetic restoration.
  2. No visible air in the repaired break.
  3. No shiny black cracks in the impact area.
  4. Little visible distortion.Good optical clarity.
  5. Smooth outer surface area.

International Windshield Repair Testing

One Test is specifically designed to test the comprehensive requirements for windshield repair systems. That test is the British Standards Test AU-251 (1994). The AU-251 evaluates the effects of high humidity, high temperature and radiation on repairs. It establishes criteria for visual appearance, optical distortion and light scatter. It also tests for impact resistance and shear strength.

Other tests do exist. They are also valuable but are less comprehensive than the British AU-25 1. Among the most important of these tests are:

  • ANSI Z26.1 (1996). Impact Test.
  • ANSI Z26.1 (1990). Test 5.12. Impact Test on Repairs- Moisture Intruded Laminates.
  • German TUV. Impact Test.
  • Australian/New Zealand Standard AS/NZS 2366.1:1999. Shear Strength of Repair Resins.
  • NWRA/NGA ROLAG Standard

Restoring the windshield's structural strength is a top priority for insurance companies because structural strength relates directly to the safety of the insured. The average tensile strength of windshield glass is between 6,000 and 10,000 pounds per square inch (psi). The strength of a damaged windshield is obviously less. Therefore, the challenge facing a repair system is to repair the windshield and return its strength to that approaching or equaling its undamaged strength.

Structural Strength is usually measured by "Impact" testing which compares the results of a steel ball impacting both a new and a repaired windshield. If a testing agency certifies a repair procedure as passing its impact test, you may conclude the repair system has restored the damaged windshield to acceptable levels of structural strength.

Optical clarity of the repair resin is a second important test. If the refractive index of the repair resin matches the range of glass being produced for laminated windshields, resin will pass its optical clarity test and - all other things being equal - the completed repair should be almost invisible.

Distortion is measured by projecting an image through the test laminated glass and onto a screen. Projecting the same image through a repaired portion of the same test glass is then measured to detect any differences or distortions. An absence of significant distortion results in the repair passing the test.

The act of passing tests in tensile strength, optical clarity, and optical distortion is not an absolute scientific guarantee that every repair conducted by a given windshield repair company will satisfy the end user. There are too many variables to make such a generalization. However, the failure to pass a generally accepted industry standard test, or, the failure to submit a repair system for such testing is a consideration which should not be overlooked in deciding which repair system to use.

Selecting A Windshield Repair Company

The selection of a professionally competent windshield repair company becomes easier if the customer knows what to look for.

Technical Training
Every windshield break is as distinctive as a person's fingerprints. The number of different repair situations to which a technician will be exposed makes factory training important. Home study courses, while helpful for review, are generally viewed as insufficient preparation. Ask vendors to describe their training program. If in doubt, request a demonstration.

Automobile and glass manufacturers regularly produce innovations in glass technolo-gy. Determine if the repair vendor maintains research and development facilities to support its field technicians. It is appropriate to ask what contributions the company has made to industry technology.

How long has the company been in business and what major accounts does it service? The reputable company will gladly provide references.

Promises do not constitute repairs. Determine if the company is providing a rate of repair (versus replacement) which meets the needs and expectations of your company. Checking references is appropriate and acceptable.

Some vendors buy and use commercially available resins which were never intended for use in windshield repair. Degradation or yellowing of the resin can undermine the repair. While you may not understand the chemical formulation of the resin, you can ask the vendor for a fleet customer reference who can document the durability of the resin. Also, check the vendor's warranty policy.

Tests can be designed to show whatever a company wants to show. The results may have little or nothing to do with the purpose of windshield repair; which is to restore structural integrity to the glass. Be sure the tests referenced are meaningful. If unsure, call several windshield repair companies.


Auto makers use urethane adhesive to bond the windshield to the body of your car. The windshield provides major structural strength. It helps support your car's roof if your car rolls over. It also keeps all of you in the car.


This rear window was installed properly and as an integral structural part of the vehicle it provided strength to the roof, which prevented it from being crushed completely in this accident.

There are stiff requirements imposed upon the manufacturers of motor vehicles by the Federal Motor Vehicle Safety Standards. Vehicle manufacturers must certify each make and model of car to a specified roof crush test (FMVSS 216) and windshield retention test (FMVSS 212). Both the adhesive and the installation process must pass these actual destructive tests.

When you replace the windshield, be sure it is bonded only with the same adhesive approved for the original installation. Silicone and butyl were once the most commonly used sealants. Urethane adhesive, which is 90 times stronger than silicone or butyl, is used for most cars today.

Most auto glass installers are concerned about passenger safety . They use an adhesive to replace your glass with bond strength equal to that of the manufacturer's original installation. Some installers use a replacement adhesive that is not certified to pass Federal Motor Vehicle Safety Standards testing. Even worse, they advertise passing FMVSS 212 and ignore FMVSS 216. Be sure to ask.

For safety in meeting both retention (FMVSS 212) and roll-over (FMVSS 216), it takes time. The longer the urethane cures, the stronger the bond and the safer the car. Safe drive away time depends on temperature and relative humidity. The installer can show you the results of typical tests run at 70°F and 50% RH. And for the next two or three days after drive away, it is recommended to open windows slightly and to avoid slamming doors or washing the car. Professional installers may suggest additional safety precautions.



BY MIKE ALLEN, Illustrations by Ron Carboni and Russell J. Von Sauers





It's a fine day. The sun is shining, traffic is moving along smartly and you haven't a care in the world. Whack! Until now, that is. Now there's a rosebud the size of a quarter smack in the windshield. What's worse, it's directly in your line of sight. It must have been a hypervelocity railgun pellet fired at you by an Imperial Stormtrooper, because you didn't see it coming or going. And as your heartbeat returns to normal, the awful truth soaks in: You're going to have to have the windshield replaced. This means dealing with the glass shop, being without your car for a day or two, having a potentially leaky windshield and, worst of all, higher insurance premiums.
Actually, it's worse. Some insurance policies won't even cover chipped glass. Maybe if you just raised or lowered your seat an inch so you didn't have to look right through the chip …

Better Living Through Chemistry

Many chips will be repaired almost completely by adhesive injection kits. But some damage requires complete windshield replacement.

Before you panic, drive home and get out your magnifying glass. Take a really close look at your new chip. It just might be possible to repair the chip instead of replacing the entire windshield. The technique is to inject an epoxy or acrylic adhesive or filler into the chip.
Even if your chip isn't in your direct line of sight, it's a good idea to try and repair it. Water will find its way into the chip, pulled in by surface tension. If the chip goes all the way through the top lamination, any moisture that gets that deep can delaminate the glass from the center membrane. Eventually, the membrane will fog, causing a larger blemish. Water also can freeze in the chip, causing a larger flaw or even a crack. Also, water can carry dirt into the crack–and there's no way to flush it out.
As you can surmise, it's best to do the repair as soon as possible, assuming that it's repairable. Remember that not all chips can be fixed. The best you can hope for is to fill most of the chip. It may still leave a visible flaw. But the improvement on most chips will be dramatic, and at least you've sealed the chip from the atmosphere and probably eliminated the possibility of it growing larger or discoloring in the future.
You can't fix long cracks. So it's critical that you fill chips before they turn into cracks. Basically, any chip that goes into the surface of the glass perpendicular to the surface or at a shallow angle can be repaired. That includes cone-shaped chips, leaf-shaped chips or almost any chip that hasn't flaked a big piece of glass off onto the road.

Let's Go Shopping

Take care to burnish the adhesive patch to a perfectly clean windshield and adapter, or you'll make a mess later.

Windshield crack repair kits can be found in the auto parts department of many mass merchandisers like Kmart, Sears and Wal-Mart, as well as more traditional auto parts stores like Pep Boys and AutoZone. Failing that, the warehouse-distributor auto parts stores that cater to professional mechanics can supply you.
In the New York area, we found two different types of repair kits and there may be others. Expect to pay around 10 bucks. Procedures differ marginally, but the principle is the same. We fixed a couple of windshields, and the results were excellent.

How Dry I Am

Start with an absolutely dry windshield that's somewhere near room temperature. Tough on a rainy or wintery day, so you may need to park your car indoors for a while to equilibrate. Dry is really essential–you don't want to trap any water in the repair. Use a hair dryer if the window is wet. If the surface is dirty, don't use any detergents or window cleaner. Lighter fluid or acetone can help dry and clean the surface, but don't use so much that it dribbles down the glass and peels the paint, or worse.

Chips Ahoy

We first used a simple kit from Loctite with a one-part adhesive and an uncomplicated syringe to apply it. Start by peeling off the backing film on one side of the precut adhesive strip and applying it to the precleaned glass, centered over the chip. Burnish with the back of your thumbnail or a blunt object. Now peel the remaining film. Orient the plastic adapter so that the fitting is as close to vertical as possible and stick it to the film. Burnish again.
Pull the cap off the syringe, keeping it pointy-end up so the adhesive doesn't wind up on the fender. Attach the syringe to the adapter. Now here's the tricky part–lay your watch down somewhere so you can see the second hand. Grasp the syringe body with one hand to stabilize it, and pull the handle of the syringe out as far as it will go. Because you've taken your watch off, you can hold the handle in this position for a full minute. This pulls a partial vacuum in the syringe–and in the crack. While you're holding this vacuum, the air in the crack bubbles up through the adhesive in the syringe, while adhesive creeps down toward the glass and chip.

Laminated Safety Glass

Ordinary window glass, like you have around the house, is pretty amazing stuff. It's clear, strong and cheap. But it's also brittle, shattering into long, dangerous, wickedly sharp shards when overstressed. Plastics would be as strong, but not nearly hard enough to resist scratching and remain clear enough for a car window–just look at any plastic-glazed outdoor bus stop or phone booth, with its patina of fine scratches. For the side windows of cars, automakers have come up with a good compromise: tempered glass. It's stronger thaimgn standard, but more importantly, when it does shatter it breaks up into small granules. These granules are still sharp, but should do less damage than the long shards of untempered glass. However, for a windshield, constantly bombarded by pebbles, tempered glass would have a short life span.
So, many years back, the car manufacturers switched to a laminated glass sandwich for the windshield. It's a simple process. Two thinner sheets of glass are fused to a rubber inner layer. The tempered-glass outer layers are then independent of each other. The rubbery center sheet provides damping to any shock waves from errant stones, reducing the probability of breakage. And if the glass is hit by an object smartly enough, odds are that only the outer sheet will break, as is the case with most stone chips. If a really big piece of debris hits the glass hard enough to break both inner and outer layers, the tough membrane prevents it from winding up in your lap. Even better, the shards of glass from the inner lamination wind up stuck to the membrane, keeping them from spalling away from the windshield at a high velocity, causing great havoc.

Now let go of the handle. Don't follow the handle, let it go abruptly. The pressure wave from the handle slamming down will force adhesive into the crack. Repeat this suck-and-slam operation a half-dozen times or so, forcing the crack virtually full of adhesive.
Now remove the syringe, adapter and adhesive sheet. There will be a film of adhesive on the surface of the glass. You can chase that back with an alcohol-dampened paper towel, but leave the pimple of adhesive right above the crack undisturbed until it cures for a few hours.
With the pimple hardened, simply take a single-edge razor blade and shave the protruding adhesive off. Use a sharp blade, and you'll be able to do this in a single pass.

The Other Path

We tried a different crack repair kit as well. This differed in that it used a two-part adhesive. This required us to mix two small vials of adhesive and hardener in the syringe before starting, which was simple. The adhesive disc and syringe adapter were similar (if not identical) to the simpler kit's, and were applied in an identical fashion. The syringe, however, was more complex. It used a wire latch arrangement on the body that dropped into two notches on the handle when necessary. A simple pushpin stuck into the body was used as a very crude valve to let air in and out of the body. Once the syringe is attached to the adapter (the adapter already being stuck airtight to the glass), the pushpin is removed. Now bottom the syringe plunger, pushing the air out. Insert the pin, and pull the handle out until the clip clicks into the slot. This will hold the plunger out, and the partial vacuum under it for the designated time.
Now, rather than rapidly releasing the pressure like we did with the earlier kit, remove the pin, admitting air into the syringe barrel. Now replace the pin, sealing the hole. Release the clip, and push the handle in, lightly pressurizing the barrel and forcing adhesive into the chip for a minute or so. The second slot will trap the clip as soon as you've pushed in far enough. Repeat this "vent, suck, vent, squeeze" operation several times to force adhesive into the crack.
While the ingenious clip-and-slot and vent business relieves you of the necessity of constantly grasping the syringe barrel like it's the last beer at the picnic, there are caveats. The vacuum pulled isn't as good, purging less air on every iteration. And the simpler kit seemed to force the adhesive deeper into the crack faster by using the plunger as a piston to rapidly pressurize the system.
Having said that, both kits did a bang-up job. After shaving the excess adhesive off, both cracks are barely visible. The adhesive is clear, and has the same refractive index as the glass so that it renders the crack invisible from almost any angle.
One warning: Don't get cute and try to depress the plunger by hand and squeeze the adhesive deeper into the glass with either kit. The adhesive patch might become unglued and squirt adhesive all over your windshield and fender and shirt. Don't ask how we know this.



It is worth the wait!

Who better to replace your windshield than the pro's at LEAKPRO® who are trained in windshield replacement by Ford and General Motors. We offer a lifetime warranty on leaks and workmanship. We also offer one free stone chip repair for one year on each windshield we have replaced if needed.

For the best windshield repair, call the windshield pros at LEAKPRO® !


ABC's 20/20 Article

(ARA) - ABC's 20/20 news magazine has concluded unsafe windshield installations can cause unnecessary deaths and catastrophic personal injuries.

"Windshield is an outdated, misleading term, says Leo Cyr, Vice President of Marketing for NOVUS Windshield Repair. "Bumpers still bump and brakes still brake but windshields have evolved from passive weather barriers to indispensable components in the structural integrity and safety of a vehicle's passenger compartment."

35 million crashes and $9 billion in annual repairs have influenced insurance companies to seek creative ways to reduce costs. However, "windshields, seat belts and airbags are inappropriate cost-cutting targets," says Cyr, "because each is an integral component in the vehicle's engineered system for passenger protection. If one fails, vehicle occupants are at risk."

Safety experts agree with 20/20. Optimum consumer safety is achieved when the factory's original windshield installation is preserved. Two conclusions are unavoidable:

1.) Damaged windshields that can be repaired should be repaired to preserve the OEM windshield and the factory safety seal.

2.) Windshields damaged beyond repair must be replaced using materials and techniques which approximate factory conditions as closely as possible.

Arnold Diaz, the reporter on the February 25 edition of ABC Television's 20/20" concluded, "A windshield can be as important to auto safety as seat belts, air bags and anti-lock brakes. But installation is key: the difference between a properly affixed windshield and a poor job can be the difference between life and death."

When Barbara Walters asked Diaz, "What about asking your insurance agent to recommend a reliable installer," Diaz responded, "That could be a problem because sometimes they (agents) steer you to a place that does it cheap and that means they could be cutting corners."

Cyr disagrees with Mr. Diaz' conclusion. "A few years ago, agents did use their knowledge and experience to provide policyholders with a choice of several responsible auto glass companies. Personally, I liked that system because my agent knows the quality of work produced by every glass shop in town. She has a vested interest in ensuring my satisfaction because she wants me to renew my policy next year," Cyr says.

Contrary to 20/20's conclusion, few agents today are empowered to refer customers to glass shops. They are instructed by their companies to have customers call a centralized glass claims processing center. The center actually assigns a shop to perform the work. If the customer has a preference of glass shops that preference is supposed to be respected.

The problems reported by 20/20 occur primarily because "most motorists are not glass experts so assessing the quality of the glass and the installation is a problem," says Cyr. Insurance companies have contractual commitments with policyholders to restore their property to pre-damaged condition. But replacing a windshield is not like replacing a bumper. Consumers rarely know if substandard materials or procedures are used on their vehicles.

Cyr advises, "Motorists can protect themselves in several ways. First, any windshield that can be repaired should be repaired. That saves both the windshield and the factory's seal of windshield to auto body. Second, if the windshield must be replaced, be emphatic and insist on an OEM or equivalent windshield that is properly installed by a reputable glass dealer. If you are unsure who is reputable, ask for the names of several glass shops in your area. Check with the Better Business Bureau. Call your own insurance agent - and even several others - and ask who they use. Finally, ask if the installer is certified by the National Glass Association (NGA)."

Cyr, who is also Chairman of the NGA Windshield Repair Technician Certification Committee, cautions that "No certification program, auto glass or otherwise, is an iron clad guarantee. Our testing can only show that a technician has the knowledge to perform a safe and effective repair or replacement. It cannot guarantee that the knowledge is fully and properly utilized on every job.

The fact is there are thousands of responsible glass shops and tens of thousands of conscientious windshield installers in the United States. Because a properly installed windshield can save your life, people should invest a few minutes to check glass shop references just as they would a surgeon's references before surgery.

Of course, you may be able to avoid surgery on your car's windshield. Cyr strongly advises that windshields only slightly damaged by rock chips, scratches and cracks be repaired. "Repair not only eliminates unsightly flaws, preventing further spread, it also allows you to keep the factory installed windshield, which is safer, sounder, leak proof, etc. That is always the better option when possible," concludes Cyr.who is also Chairman of the NGA Windshield Repair Technician Certification Committee, cautions that "No certification program, auto glass or otherwise, is an iron clad guarantee. Our testing can only show that a technician has the knowledge to perform a safe and effective repair or replacement. It cannot guarantee that the knowledge is fully and properly utilized on every job.



Aired on Market Place: October 24, 1995

The windshield in a car does more than keep the wind and rain out. It also helps protect you in case of accidents. It will keep a passenger inside the vehicle and prevent an ejection. In case of a rollover it also helps maintain the structural integrity of the roof. But a lot of shops are installing replacement windshields the wrong way. The adhesive they use is not the proper one, or they don't allow it to cure properly. In order to save a few dollars they are jeopardizing people's lives.

More Information:
Depending on the make and model, a windshield provides anywhere from 18 to 20 percent of the structural integrity of the vehicle. Passenger-side air bags rely on the windshield for support. If the windshield pops out during an accident the air bag will inflate out onto the hood of the car and become totally ineffective. That's just one more reason why it is important to have the windshield installed properly. The air bag inflates with such power that if the windshield hasn't been installed properly it can push the windshield right off the car. Also the structural support the windshield provides could prevent the roof from caving in on the passengers during an accident. A cave-in could inhibit any help, i.e. firefighters, from getting a passenger free from the vehicle.

Close to a million windshields are replaced each year in Canada. Thousands of those are installed improperly. A windshield is not difficult to install. There are steps which should be followed to make sure it is done right: the old adhesive has to be taken off; primers need to go on the body and on the glass; then the adhesive, urethane, is applied; and the windshield is put in place and left to sit so the urethane can cure. Curing time is one of the major problems with improper installations. Many installers don't let cars sit long enough to make sure they're safe to drive away. If it is not properly cured the urethane will be wet in the centre. This means weak points and the windshield will let go at its weakest point. Urethanes need up to six hours to cure safely. For maximum protection, to prevent roof crush, urethane has to cure for 24 hours, a lot longer than that in the winter. But for most shop owners time means money and annoyed customers.

There are government standards which govern the installation of windshields when a vehicle is being manufactured but these regulations do not legally apply to replacement windshields or after-market installations. The goal of these standards is to reduce crash injuries and fatalities by making sure as much of the windshield stays attached to the car as possible. Body shops and glass shops can be, and have been, held liable when they don't follow the vehicle manufacturers replacement recommendations.

Some shops don't even use urethane. To cut corners and save money they use things like silicon, bathtub caulking, and various types of adhesives that we don't even recognize to hold the windshields in place. The most common is Butyl. Butyl was used in the early 1970's but it is only a sealant not an adhesive and it never cures. Butyl is half the cost of urethane. But with Butyl there is no strength, it just pulls apart.

There are no government regulations which require an autoglass installer be certified or trained. To combat lack of training the National Glass Association in the United States established a certification program. Also, the glass division of the Ford Motor Company, called Carlite, holds one week installation schools throughout the year which are available free to anyone working within the industry.

So if you have a windshield that needs to be replaced, try to get it replaced the same way the car-maker installed it.


  • Ask the shop if they follow the car-maker's specifications.
  • Make sure they use urethane.
  • If they keep the car for only a short time, ask questions.
  • Find out what the proper cure time is for the adhesive they use.
  • Remember it takes 24 hours - longer in winter - to reach a full cure.
  • If the shop tells you they use Butyl, take your car elsewhere.