If you have a large crack in your car's windshield, then you may need to have the entire windscreen replaced. This depends on the size of the crack, the location, and the depth. If you are lucky enough to have windshield damage that falls into the category of cracks and chips that can be fixed, then you luckily will not even need to have a full replacement completed. A simple crack repair can be arranged instead, especially if the crack is not in the line of sight of the driver, less than 18 inches long, and shallow. However, if you do not intend on having the crack repaired for a few days or even a few weeks, then you will need to keep the crack from spreading.
Cracks that form in a windshield generally have two separate ends that spread out across the surface of the glass. The crack spreads due to the structure of the glass itself. Glass is formed from a liquid silica or sand material that hardens as it cools down. However, the hardening process does not create a completely solid material. Instead, the windshield becomes an amorphous solid that retains some properties of a solid as well as some of a liquid. Much of the structure of the glass actually forms crystalline bonds. These bonds are weakened by the pressure from the crack edges and this forces the crystalline bonds to break apart allowing the crack to spread.
One of the best ways to stop the crack from spreading is to create a rounded end on both the right and left edge of the crack. A drilled indentation or small hole can work for this. You will need to purchase a very small drill bit that is quite strong to create the indentations. You can buy either a tungsten carbide or a diamond tip bit. A spear shaped bit is a good choice too, and so is a product that is about one-sixteenth of an inch in diameter.
Once you have your drill bit purchased and secured to your drill, hold the drill so the bit is perpendicular to the windshield. This will help to create a straight and consistent opening. Use the lowest drill speed you can and place very slight pressure against the windshield as the bit rotates. You want the bit to pierce just the outside glass layer of the windshield, which is only about 0.76 millimeters thick. This means that an indentation that is around one-half of a millimeter deep is sufficient.
When you are done drilling, use a damp cotton cloth to wipe away any glass residue that is left behind.
Cover the Crack
After you drill the holes on either side of the crack, you will need to cover it. This will prevent dirt and debris from entering the opening. This debris can vibrate inside the crack when the car moves, and the extra pressure may force the crack to widen or form secondary cracks to relieve the stress. You can use a piece of clear packing tape to cover and protect the crack. You will first need to clean the damage. Soap and water are not ideal in this situation, because these materials will generally remain in the crack and cause pressure and stress issues much like dirt and debris. To avoid this problem, squirt some lighter fluid in the crack to flush out foreign matter. The fluid is a liquified gas called butane that evaporates quickly.
Using Tape or Glue
Once the crack has been cleaned, cut a piece of packing tape that is two inches longer than the crack. Center the crack in the middle of the tape and press if down with your fingers. You also have the option of filling in the crack with glue. An industrial strength glue called E8000 is ideal for this. This glue is a quick drying, all-purpose glue that can be found at both hardware and craft stores. Place a small amount of the glue on a toothpick and force it into the windshield crack. If you do this, just make sure to tell the windshield repair specialist when you do get your windshield fixed. Acetone will be needed to remove the glue.
For more information about windshield repair, check out websites like http://www.centralglassutah.com.