Fixing a chip in a windshield is fairly easy, but a crack can be much more difficult. Not only do you need to fix the damage that was already done, but you also have to stop the crack from spreading. Take your time and be sure to fill every centimeter of the crack with resin, or else your repair will not be successful.
Look at the crack. Is it a small chip or a running crack? Determine how big it is and how many branches it has. The bigger the crack and the more running branches, the more difficult it will be to fix. Simple chips are the easiest type of car window damage to fix.
Drill a hole halfway through the glass at each end of the crack using a diamond drill bit. The hole should run as deep as the crack. Follow the link in Resources for more details.
Use a clean cloth to apply acetone to the crack, the holes and the surrounding area. Then, use the edge of a razor blade to dig out stray pieces of glass. You probably won't be able to get every particle of glass out of the crack, but the cleaner it is, the better it will look once it is fixed.
Attach the alignment tool from your windshield repair kit directly over one of the drill holes. Attach the suction cups to the window so that the threaded hole is above the spot where you drilled.
Screw the repair tube in as tightly as possible. Then, drop in 2 to 4 drops of resin.
Quickly screw the plunger in until it is tight. Unscrew it for about 20 seconds to let any air bubbles get out. Then, screw it back down again. Wait for a minute.
Put finishing film on top of the hole and leave it there for at least 10 minutes.
Repeat steps 4 to 7 at the other drill hole and at the central chip where the window is cracked.
Fix the narrow parts of the crack. Put resin on the edge of the razor and push it down into the gap. Then, use the side to smooth the resin along the top of the crack.
