Understanding Windscreen Crack Progression
You may see a chip on your windscreen that’s no bigger than a 20p piece. It’s small, it’s not in your direct line of sight, so you tell yourself you’ll get it sorted next week.
That’s usually when things go wrong.
How Quickly Can a Chip Become a Crack?
The honest answer is: faster than you’d think. We regularly see customers whose small chip has spread into a 15cm crack within 48 hours. Temperature is the main culprit. On a sunny day, your windscreen can reach 65°C on the outside whilst the air conditioning keeps the inside at 20°C. This temperature difference creates stress across the glass, and that stress finds the weakest point: your chip.
Cold weather is just as bad. If you’ve got a chip and temperatures drop overnight, the glass contracts. Pour hot water on your windscreen to clear ice (which you shouldn’t do anyway) and you’re asking for that chip to split into a proper crack.
The Real Cost of Waiting
Most people don’t realise that windscreen repairs are cheap. If you catch damage early many insurance policies cover the cost with no excess. You can often get it done at your workplace or home within a day or two.
Wait too long, and you’re facing a full replacement. Depending on your vehicle, that’s £200 for an older car, but easily £500-800 for anything with rain sensors, heated windscreens, or head-up displays. Modern windscreens aren’t just glass, they’re calibrated for your car’s safety systems. Replacing them properly takes time and specialist equipment.
Read: How to Tell If You Need Windscreen Repair or Replacement
MOT Failures and Legal Issues
A crack longer than 40mm in the driver’s swept area (the section cleared by your wipers) is an MOT failure. If it’s anywhere else on the windscreen and longer than 100mm, that’s also a fail. Police can issue fixed penalty notices for driving with a damaged windscreen that impairs your vision.
More importantly, your insurance could be void if you have an accident with a damaged windscreen. Insurance companies can argue you were driving an unroadworthy vehicle, which means they won’t pay out.
Windscreens Don’t “Self-Heal”
Some people think if a chip hasn’t spread after a few days, it never will. That’s not how glass works. The damage is still there, weakening the structural integrity. Every pothole, speed bump, and door slam creates tiny stress fractures around the chip. You might not see them, but they’re there, waiting for the next temperature change or vibration to connect them into a visible crack.
What Happens During a Repair?
Professional windscreen repair involves drilling out the damaged area, injecting resin under vacuum pressure, and curing it with UV light. The process takes about 30 minutes and restores roughly 80-90% of the windscreen’s original strength. You’ll still see a slight mark if you look closely, but it won’t spread and it’s perfectly safe.
The catch is that repairs only work on chips smaller than a £2 coin. Once cracks start spreading, the damage is too extensive and replacement becomes necessary.
Our Advice
If you get a chip, get it looked at within 24-48 hours. Don’t wait for your next service or until it’s more convenient. We’ve seen too many customers who could have had a simple repair end up paying hundreds for a replacement because they delayed a few days.
Ring us on 01279 870 001 or book online. We’ll come to you, assess the damage honestly, and get you back on the road safely. If it’s repairable, we’ll tell you. If it needs replacing, we’ll tell you that too. What we won’t do is let a small problem become a big one.
Jay & Rob’s Windscreens
Mobile Service Across Essex & Hertfordshire
01279 870 001