Should I repair a windscreen chip or replace the screen?
Why a small chip is worth fixing this week rather than next month, the MOT limits that decide repair from replacement, and what changes if your car has a camera behind the glass.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 4 min
- Safety
- caution
Short answer
A chip smaller than a 20p coin can usually be resin-repaired in half an hour, and most comprehensive insurance policies cover repairs with no excess and no effect on no-claims — so there is rarely a reason to delay. Once a chip has spread into a crack, or sits in the driver's swept vision area above the MOT size limit, it becomes a replacement. Cold weather and demisting a frozen screen are what turn chips into cracks.
A modern windscreen is laminated: two layers of glass with a plastic interlayer that holds it together. A stone chip damages the outer layer and leaves a small void, and that void is a stress concentration. Anything that flexes the glass or creates a temperature difference across it — a pothole, a slammed door, a hot demister blasting a frozen screen — can turn it into a running crack in seconds. That is why the advice is always to repair early, and why chips so often become cracks in the first frost of the autumn.
Safety
Step by step
- Look at where the damage is, not just how big it is.The MOT divides the screen into zones. In zone A — the area swept by the wipers directly in front of the driver, defined as a 290 mm wide band centred on the steering wheel — damage larger than 10 mm is a failure. Elsewhere in the swept area the limit is 40 mm. This is the single fact that decides repair from replacement.
- Measure it against a coin.A 20p coin is roughly 21 mm across and a £1 coin is roughly 23 mm, so either gives you a quick sense of scale. Most repairers will attempt a chip up to about the size of a 20p, provided it is not in the driver's critical zone and not at the edge.
- Check whether it has legs.A clean bullseye or star chip with no cracks running from it is the best candidate for repair. Once cracks have started to run, and especially if one reaches the edge of the glass, the screen has lost integrity and needs replacing.
- Ring your insurer before paying.Most comprehensive policies include glass cover, and repairs are commonly free with no excess and no claim recorded against your no-claims discount. Replacements usually carry a glass excess. Either way, it is worth two minutes on the phone before booking privately.
- Protect it in the meantime.A piece of clear tape over the chip keeps dirt and water out, which matters because a contaminated chip repairs less well and looks worse afterwards. Avoid blasting hot air straight at a frozen screen, avoid slamming doors with the windows up, and take speed bumps gently.
- Ask about cameras and sensors before booking a replacement.Many cars have a forward-facing camera for lane keeping and emergency braking mounted behind the screen, plus rain sensors and sometimes a heated element. A replacement needs the camera recalibrated afterwards, which is a specific job — confirm the fitter does it, because an uncalibrated system can behave incorrectly.
- Get a repair done sooner rather than later.Repairs work by drawing air out of the void and injecting resin. The longer a chip sits, the more dirt and moisture get in, and the less invisible the finished repair.
Common mistakes
- Waiting to see whether it spreads — It will, and the trigger is often something as ordinary as a cold night. A repair is cheap, quick and usually free on insurance; a replacement is neither.
- Using a supermarket DIY repair kit on a chip in the driver's eyeline — Those kits can work on minor damage away from the critical area, but a poor result in zone A can leave distortion exactly where you look, and it may then be beyond a professional repair.
If it doesn't work
Chip appeared and by the next morning it is a crack
Cause: Thermal stress overnight, or on demisting — Fix: Too late for a repair in most cases. Warm the screen gradually in future rather than aiming hot air directly at frozen glass.
Repair done but you can still see a mark
Cause: Normal — repair restores strength and stops the spread, it does not make damage invisible — Fix: A good repair leaves a faint blemish. If it is in your eyeline and distracting, discuss replacement, but the repair has done its structural job.
Crack running from the edge of the screen
Cause: Edge damage or body flex — Fix: Replacement. Edge cracks compromise the bond between glass and body, which matters for roof strength and airbag support.
Chip is right on the black band at the edge
Cause: Damage in the frit or bonding area — Fix: Usually not repairable, because the resin cannot key properly and the area is structurally important.
New screen fitted and there is wind noise or a leak
Cause: Bonding or trim not seated correctly — Fix: Go back to the fitter. A screen is bonded structurally, and a poor bond is a safety matter rather than a comfort one.
Questions people ask
Will a chip fail an MOT?
It depends on size and position. In the 290 mm zone directly in front of the driver the limit is 10 mm; elsewhere within the wiper-swept area it is 40 mm. Damage outside the swept area is generally not assessed.
Does claiming for a windscreen affect my no-claims?
For repairs, almost never — most insurers treat them separately and free of excess. A full replacement is normally a glass claim with its own excess and does not usually affect no-claims either, but the policy wording is what counts.
Can any chip be repaired?
No. Position, size, contamination, and whether cracks have started all matter. A chip directly in front of the driver, one at the edge, or one that has already run is usually a replacement.