A stone chip is the most common piece of glass damage there is, and most of the time it is also the cheapest to deal with, provided it is dealt with early. This guide explains how we decide between a repair and a replacement, so you know what to expect before you call.
What a repair actually does
A chip repair does not make the damage disappear. The technician cleans the impact point, draws the air out of the break under vacuum, then injects a clear resin that fills the fractured glass and cures under UV light. Done well, the repair restores the structural strength of the glass, stops the chip from spreading into a crack, and leaves a faint mark that is far less visible than the original chip. It takes well under an hour and the vehicle can be driven straight away.
The four things that decide it
Size
The usual rule of thumb is that a chip smaller than a loonie, or a crack shorter than about 15 cm (6 inches), is a candidate for repair. Bigger than that and the resin cannot reliably restore the glass, so the windshield is replaced.
Position
Damage directly in the driver's line of sight is treated more cautiously, because even a good repair leaves a slight distortion and that is the one place on the glass where it matters. Damage that reaches the edge of the windshield is also a replacement more often than not: the edge is where the glass carries load, and cracks that start there tend to keep going.
Depth
A windshield is two layers of glass laminated around a plastic interlayer. A chip that has only damaged the outer layer repairs well. If the break has gone through to the inner layer, or the inner layer is cracked, the glass needs to be replaced.
Age of the damage
The longer a chip is open to the weather, the more dirt and moisture work into the break. Contaminated chips repair less cleanly and are more likely to spread first. A chip that is repaired within a few days is nearly always a better result than one repaired a month later.
Why chips turn into cracks
Glass expands and contracts with temperature. A chip is a stress point, and the daily swing between a cold night and a warm defroster, a hot dashboard and a cold rain shower, or a pothole hit at the wrong moment, is often all it takes. Winter is the worst season for it, which is why a chip picked up on the highway in November tends to become a crack in January.
If it is a replacement
Replacement is a bigger job than it used to be, for two reasons. First, the windshield is bonded to the body with urethane adhesive and is part of the vehicle's structure: it supports the roof in a rollover and gives the passenger airbag something to deploy against, so the adhesive has to be applied properly and given time to cure before the vehicle is driven. Second, many vehicles built in the last decade have a camera mounted behind the glass for lane-keeping, adaptive cruise control or automatic emergency braking. When the glass is replaced, that camera usually has to be recalibrated so it sees the road correctly. If your vehicle has any of those features, tell us when you request a quote and we will explain what the job involves for your model.
What to do right now
Keep the chip clean and dry if you can. A piece of clear tape over it will keep dirt out until it is repaired. Avoid slamming doors, blasting the defroster on a frozen windshield, or running the vehicle through a car wash. Then send us a photo with a coin beside it for scale, along with the year, make and model, and we will tell you which way it is likely to go.