Our busiest weeks of the year for windshield replacement are the first cold snaps in November and December. They are not busy because of new damage. They are busy because chips that sat harmlessly all summer suddenly run into cracks. Here is why that happens and how to avoid being one of those calls.
The physics of a chip in winter
A windshield is two layers of glass laminated to a sheet of vinyl. A stone chip is a break in the outer layer. In summer the chip is stable; the glass is at a fairly even temperature and nothing is pulling on the break.
Winter changes that in three ways.
Thermal shock. The car sits overnight at -20°C. In the morning you start it and turn the defroster on high. The inside surface of the glass warms quickly while the outside stays frozen. The two layers expand at different rates, and the chip is the weak point where that stress concentrates. Many cracks start in the first five minutes of a cold morning.
Ice in the break. Moisture gets into the chip during a thaw, then freezes and expands overnight. It is the same process that breaks up asphalt, on a much smaller scale, and it wedges the break open a little further each night.
Mechanical shock. Potholes and frost heaves flex the body of the car, and the windshield flexes with it. Ottawa's roads in February are a stress test for a windshield that is already compromised.
Why it matters for cost
A chip is a 30-minute repair, and most Ontario comprehensive policies waive the deductible for it. A crack that has reached the edge of the glass is a full replacement, and on any vehicle with a windshield camera, an ADAS recalibration on top. The difference is a few hundred dollars of deductible at minimum, and the difference in time is an hour versus half a day.
The pre-winter checklist
- Look at the glass in good light. Stand outside the car and look across the windshield at an angle. Chips are easy to miss from the driver's seat.
- Check the edges and the wiper sweep. Edge chips are the ones most likely to run, and cracks in the wiper sweep are the ones that get you a ticket.
- Repair anything you find, now. Smaller than a toonie and away from the edge is a 30-minute repair, mobile or drop-in.
- Replace worn wiper blades. A hard, cracked blade chatters across the glass and can drag grit through a chip.
- Warm the car gradually. Start the defroster on low and let the cabin warm before turning it up. It is gentler on the glass and on you.
- Never pour hot water on a frozen windshield. It is the fastest way to crack one, chip or no chip.
If it has already cracked
A crack that starts away from the edge and is shorter than a business card can sometimes still be repaired. Beyond that, it is a replacement, and the sooner the better: cracks grow, and a crack that crosses the driver's view is a ticket risk under the Highway Traffic Act. We do winter replacements every day, at the shop and mobile with a garage or carport available. Book a slot.
Common questions
Can a chip be repaired in winter?
Yes. In the shop, always. Mobile, in most weather, with a covered spot in deep cold.
Does the defroster crack windshields?
It can trigger a crack from an existing chip by heating the inside of the glass while the outside is frozen. Warm the car gradually.
Should I use hot water to de-ice a windshield?
No. Thermal shock from hot water can crack even an undamaged windshield.
Related
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