Rock chips are unavoidable; everyone gets them. When was the last time you heard that "tick" of a rock glancing off of your windshield and thought "I'd better get that looked at", only to find a big crack in your glass the next day? Don't let a lack of time or money keep you from making a relatively inexpensive repair that could end up saving you hundreds of dollars in the long run.
Rock chips spread because glass has a "grain" to it just like a piece of wood, and once that grain is broken it creates a weak spot in the glass. Vibration from driving, pressure from heat building up inside your car, or torsion from going over an uneven bump may cause flexing in the glass that may cause it to break further along the grain. Another big danger is sudden temperature changes. Glass is like water, in that it expands when hot and contracts when cold and can actually change shape. Under time lapse photography, it has been shown that a windshield in a car that is sitting in the hot sun can expand outward as much as a quarter inch from internal heat and pressure. This expansion puts stress on the grain of the glass and "Bang!" what was a tiny chip has turned into a crack that covers half of your windshield. A rock chip repair will bond the broken area of the glass and hopefully keep the chip from spreading, although it is only a structural repair and will not greatly change the appearance of the chip or make it disappear.
Here are a few good tips to help keep your windshield intact and avoid cracking until you can get to a good rock chip repair shop to have the chip fixed.
- Roll down your windows a little bit on warm days. You don't need to lower them enough to let in rain or debris, just allow just enough a gap so that hot air inside your car can vent to the outside and pressure does not build up.
- Park in the shade if at all possible to avoid heating of the glass or of the car's interior.
- Do not subject the glass to sudden temperature changes. If the car has been sitting in the sun, turn the air conditioning up slowly so that the interior of the car does not cool too quickly. During the winter don't turn on your defroster until the interior of the car (and the glass) have had a chance to warm up gradually. Don't put your car through a car wash that uses hot water on cold days or cold water on hot days. Cold air or water on a hot windshield or vice-versa can cause a severe crack even if there is no chip!
- Try to avoid potholes, and go over speed bumps slowly and straight on to avoid jolting or twisting the windshield.
- Before taking your car in to get a chip repaired, make sure that the chipped area has been dry for at least 24 hours. On a microscopic level, water inside of a chip or crack will prevent the adhesive from bonding to the glass, and the water will be sealed inside the chip and cause further cracking. If you think it may rain before you can get to a repair shop, putting clear tape over the chip will seal out water until you can get it fixed.
Andrea Murphey writes for Diamond Glass in Utah.
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