A windscreen chip: repair or replace

A windscreen chip is the case where delay costs exactly ten times more. Repairing a chip is cheap and quick; replacing a screen on a modern car drags the electronics in with it.

Why cracks spread

A windscreen is two layers with an interlayer between them. A chip breaches the outer layer and creates a stress concentrator.

What makes it spread:

• Temperature change — hot air from a vent onto frozen glass. Cause number one.
• Washing with hot water in winter.
• Impacts and vibration — a pothole, a door slammed hard.
• Body flex over bumps: the screen is part of the structure.

So: a chip acquired in autumn survives until the first real frost and becomes a crack across the dashboard.

What can be repaired

Size — roughly up to a coin; the exact limit depends on the technique.

Type — stars, bullseyes, and simple chips without branching.

Zone — not in the driver’s line of sight. Repair leaves slight distortion, and in the critical area that is unacceptable.

Freshness — the fresher the chip, the better the result. An old one already contains water and dirt, and the resin will not fill it completely.

What cannot be repaired

A crack longer than the stated limit.

A chip in the rain sensor or camera zone — optical clarity is required there.

Damage to the inner layer.

A chip at the edge of the glass — stresses are highest there and a repair does not hold.

First aid before repair

Cover the chip with clear tape — to keep water and dirt out. That improves the chance of a good repair.

Do not wash with hot water.

Do not aim the demist straight at the chip in frost — warm the glass gradually; covered in the de-icing article.

Do not delay — a repair costs a fraction of a screen.

Replacement: why it is not just glass

On a modern car the windscreen carries electronics.

The assistance camera — after a screen replacement it must be calibrated. Without that, lane keeping, sign recognition, and autonomous braking work with an error; covered in the assistance article.

The rain and light sensor — it must be fitted precisely, or the wipers run without rain or ignore it; covered in the wipers article.

Heated wiper park area and the antenna — separate circuits.

A head-up display — it requires glass with the correct interlayer.

What follows: a cheap replacement with glass lacking the right specification leaves some systems inoperative or, worse, inaccurate.

After replacement

1. Camera calibration — ask for confirmation that it was done.
2. Read the codes — camera, rain sensor, assistance systems.
3. Test the wipers in automatic mode.
4. Do not wash the car for the first few days — the adhesive is curing.
5. Check for leaks and wind noise; covered in the door seals article.

In short

• Chips spread with temperature change; demist onto frozen glass is cause number one.
• Taping over a chip before repair improves the result.
• Repairs are not done in the driver’s sight line because of residual distortion.
• Screen replacement on a modern car requires camera calibration.
• Cheap glass without the right specification leaves assistance systems inaccurate.

Download the app — camera and driver assistance codes are read with an ELM327 adapter over Bluetooth SPP on Android.