You're driving down the highway, and come up behind a cement truck. SMACK! A piece of dried cement falls off the truck and hits the windshield, creating a bull's eye crack. Although the windshield protects you from injury, the damage has been done. Since the crack could easily spread, it should be dealt with as soon as possible.
There are a few options when repairing a nick in a windshield, depending on the size of the damaged area. Home repair kits fill the windshield with a clear resin, making it almost impossible to see and largely preventing the possibility of the crack spreading. If the bull's eye isn't directly in the line of sight, this can be a viable option. You can also have a professional do this repair for you. Although the home kits claim to be quick and easy, they don't provide the deft expertise that the practice of hundreds of repairs will provide. A home kit involves the real possibility that the repair will not work well, and then the entire windshield will need to be replaced.
Other options include having a professional fix the crack or pit, or having the professional replace the entire windshield.
In order to fill the crack yourself, get a good resin kit. The key to a successful patch job is to fix it under the right conditions. Make sure the windshield is out of direct sunlight. Clean and dry the surface, since any dirt or water will interfere with the curing of the resin. Before applying resin, the crack will need to be cleaned out. Remove any glass particles with a razor blade. Even better; use an air compressor with a hand-activated nozzle to blow away any glass chips.
A good resin kit will have an applicator that is mounted to the windshield via a system of suction cups. Put this in place, making sure that the tip of the applicator is mounted directly over the center of the pit. The best way to ensure that the applicator is in position is to check through the windshield from inside the car.
Once the applicator is firmly in place, add resin to the reservoir. It's often good to add more than the directions call for, since extra resin can easily be scraped away while insufficient resin will result in a failed patch job. Insert the plunger after the resin, and begin to screw it down. Wait a minute or two, then loosen the plunger to release any bubbles that may have formed. Screw the plunger down again, and wait a few minutes for the resin to penetrate the entire chip.
Remove the plunger, housing and suction-cup mount, and apply the clear finishing film. This will cure the resin and create a flush surface with the surface of the windshield. Apply the film from the center outwards, in such a way that bubbles do not form between the film and the windshield. Use a razor blade or other hard, flat object to fully crease the film to the windshield.
After removing the film, use a hard object that won't scratch the glass to remove excess resin. Something like a plastic scraper or piece of wood, such as a popsicle stick should do the trick.
