Prevention · 5 min read
How to Slow a Windshield Crack From Spreading
Marine-layer mornings and warm afternoons are rough on damaged glass. Here's how to keep a chip from running until a technician gets to you.
By the South Bay Auto Glass Co. team ·
Once a chip becomes a crack, it rarely stops on its own. The good news is that you can slow it down a lot, sometimes long enough to repair it instead of replacing the windshield. Here's what actually works, and why South Bay weather makes it matter.
Why cracks spread in the first place
Windshield glass is two layers of glass bonded to a plastic interlayer. A chip breaks the outer layer and leaves a weak point. Four things push that weak point into a crack:
- Temperature swings. The edge of the glass and the center heat and cool at different rates.
- Vibration and flex. Potholes, speed bumps, slammed doors and hill grades all twist the body a little.
- Pressure. Blasting the defroster or AC at the glass, or a hot car wash rinse, puts sudden stress right on the chip.
- Moisture and dirt. Water gets into the break and expands and contracts with temperature changes.
Step 1: Manage the temperature
This is the big one in the South Bay. A June-gloom morning in Redondo can sit near 60° with the glass wet, and by afternoon the same car can be parked in full sun in Gardena or Carson, where it's often 10 to 15 degrees warmer. That swing is exactly what cracks glass.
- Warm up the car gently. Start the defroster on low and let it build.
- Park in a garage or shade when you can, and use a sunshade on hot days.
- Don't aim cold AC at a hot windshield. Point the vents at your feet for the first few minutes.
Step 2: Reduce vibration
- Slow down over speed bumps and around the potholes on older streets.
- Close doors and the trunk gently. A slammed door pressurizes the cabin and flexes the glass.
- On steep grades, like the climbs up Hawthorne Blvd and Palos Verdes Drive onto the Peninsula, go easy on the throttle and the brakes.
Step 3: Keep it clean and dry
Put clear packing tape over the chip from the outside. It keeps out water, road grit and the salt film you get near the beach. Clean glass also bonds better with resin, which makes the repair more likely to work. Skip the car wash until it's fixed.
What about DIY repair kits?
A drugstore resin kit can help on a small, fresh, clean bullseye if you follow the instructions exactly. But a poor DIY fill traps air and dirt in the chip, and a professional can't redo it later. If the chip is in your line of sight, or it's already starting to run, leave it to a technician.
When to stop driving
Get off the road and call us if the crack reaches the edge of the glass, if it's in front of the driver, if it grows while you watch, or if you hear creaking over bumps. At that point the windshield isn't holding its full strength, and California law (Vehicle Code §26710) prohibits driving with a windshield that impairs your view.
Timing matters. Most chips that get repaired within a few days never need a replacement, and many insurers cover chip repair at no cost to you. Wait a month and you're usually paying for a new windshield.
