You can repair windshield cracks easily with any variety of kits sold in auto-parts stores. Unless the chip is at the edge of the glass, which can threaten the structural integrity of the window, most chips can be repaired without having to replace the windshield. What you have to learn is how to tell if a windshield chip repair is good; an improper repair may allow the chip to continue breaking into a crack. Fortunately, the process to tell if a windshield chip repair is good is simple and requires no special tools or skills.
Dry and scrape clean the area of the crack repair.
Look at the finished repair. If you can see any type of air bubble in the plastic, the repair is no good and you must reapply the plastic resin according to the directions on your repair kit.
Squeeze a small amount of Dawn Liquid dish soap onto a sponge and wipe it over the repair once you have eliminated any visible air bubbles. If you can feel anything "snag" the sponge, redo the repair, the surface of the repair should be as smooth as the rest of the windshield glass.
Blow on the repair spot with a drinking straw after you have wiped it with the dish soap and the sponge does not get snagged when doing so. When you blow air over the repair, the soap film should move away and not bubble. If it bubbles, it means the liquid soap is becoming trapped in a hole in the plastic resin and pooling. Also, watch that there is no clouding occurring in the repair from the liquid dish soap getting inside the resin and spreading.
You can also use a small amount of water that has been coloured with food dye instead of liquid soap as a quick test. Pour the coloured water on the repair and wipe it off, if the repair remains discoloured then their are cracks or holes in the repair and it must be redone.
Do not attempt to repair any windshield chip that is larger than the size of a quarter, as the damage is too great and the structural integrity of the glass is no good. Replace the windshield.