It usually starts with a sharp crack from a stone on the motorway and a small star or bullseye on the glass. Left alone, a windscreen chip can spread into a crack that means replacing the whole screen. Dealt with early, many chips can be repaired quickly and for far less.
Why chips turn into cracks
A chip weakens the glass at one point. Stress from changes in temperature, such as a hot heater blowing on a frosty screen, a cold car wash on a hot day or strong sunshine after a cold night, can make a chip spread. Potholes, speed bumps and the body of the car flexing on rough roads add more stress. That's why a chip that looked harmless can become a long crack almost overnight.
What the MOT says about windscreen damage
The MOT inspection manual sets clear limits. The key area is zone A, a 290mm wide strip of the windscreen centred on the steering wheel, within the area swept by the wipers. Under the MOT rules:
- Damage in zone A larger than 10mm in diameter is a fail
- Damage elsewhere in the swept area larger than 40mm in diameter is a fail
So a chip that's small enough to pass today can fail an MOT if it spreads. Damage that affects the driver's view of the road can also be a problem outside the MOT, so it's worth acting quickly.
Chip repair vs windscreen replacement
A chip repair involves cleaning out the damage and filling it with a clear resin, which is then cured. This restores strength to the glass, helps stop the chip spreading and makes it much less noticeable. Chip repairs are best suited to small chips that haven't started to crack.
A replacement windscreen is usually needed when:
- The chip has already spread into a crack
- The damage is large or close to the edge of the glass
- There are several chips close together
- The damage is in the driver's direct line of sight, where even a repaired chip may leave a slight distortion
What to do straight after a chip
- Cover the chip with a small piece of clear tape to keep dirt and moisture out
- Avoid blasting hot air on a cold windscreen, and avoid slamming doors
- Book a repair as soon as you can, before it has a chance to spread
Windscreen chips and lease returns
If you're handing back a lease car, the BVRLA fair wear and tear guidelines that most leasing companies use generally accept professionally repaired chips outside the driver's line of sight. Damage in the driver's line of sight is usually charged. See our lease return checklist for more.
Frequently asked questions
Will a windscreen chip fail my MOT?
It depends on its size and position. Damage larger than 10mm in zone A (the 290mm wide area centred on the steering wheel) or larger than 40mm elsewhere in the swept area is a fail.
Does my insurance cover windscreen chip repair?
Many comprehensive policies include windscreen cover, sometimes with a lower excess for repairs than replacements. Every policy is different, so check yours.
How long does a windscreen chip repair take?
A chip repair is usually a short job. We'll confirm timings when we see photos of the damage.
