A stone chip is a small thing that becomes a bigger thing slowly, which is exactly why it gets ignored. Ten minutes with a clean panel and decent light tells you whether you have something to deal with.
Where they turn up
Chips are not random — they collect where the airflow throws grit at the car:
- The bonnet, especially the leading edge. Motorway miles put them here first.
- The front bumper and lower valance. Constantly sandblasted, and often the worst area on the car.
- The leading edge of the roof and the A-pillars. Easy to miss because nobody looks there.
- Wing edges just behind the front wheels, and the sills and rear arches, where your own tyres fling grit back along the car.
- Door mirror casings and the leading edge of the door shuts.
How to look
Wash the panel first — chips hide under road film. Then use daylight, or a torch held low so the light rakes across the surface rather than shining straight at it. Chips show up as pinpoints darker than the paint around them, and a light run of your fingertips will find the ones your eyes skip over.
Straight after a wash is the natural time to do it, while the paint is clean and you are already walking round the car.
Working out how deep it has gone
Depth is what decides whether a chip matters. There are three broad levels:
- Lacquer only. A small white or greyish mark with no colour missing. The paint underneath is still sealed. This is cosmetic.
- Through the colour to the primer. Usually shows as a light grey or off-white dot. The metal is still covered, but the chip is now a step away from bare steel.
- Through to bare metal. Dark grey, near-black, or with a brown or orange tinge — and brown means it has already started to rust.
Why leaving it matters
Paint is not decoration, it is the barrier keeping water and air off the steel. Once a chip is through to bare metal, that barrier has a hole in it, and everything the road throws at your car — rain, spray, winter salt — sits in the hole.
The problem is that rust does not stay put. It spreads sideways underneath the surrounding paint, lifting it from beneath. That is why a chip you remember as a pinhead turns into a blister a few months later, then into a patch of flaking paint the size of a coin. At the pinhead stage it is a fill and a touch-in. At the flaking stage the corrosion has to be cut out and the area properly rebuilt, and that is a different job at a different price.
Aluminium panels, which a lot of bonnets now are, do not rust in the same way — they corrode to a white, powdery oxidation instead. It looks less alarming and it still needs sealing.
When to get it touched in, and when to leave it
Worth dealing with:
- Any chip where you can see bare metal, and every chip showing brown staining.
- Chips on horizontal panels — bonnet, roof, boot lid — because water sits in them rather than running off.
- Clusters on the bonnet and leading edges, where the whole area has been peppered.
- Anything you find heading into winter, when the salt goes down.
- Anything on a lease or company car, before it goes back.
Fine to keep an eye on: marks that have not broken through the colour coat. Keep the paint clean and waxed and check them again in a few months.
One honest word on touch-up pens. To seal exposed metal on a chip you have just found, a pen is better than nothing and buys you time. But the paint sits proud of the surface and you will see it, so it is a stop-gap rather than a repair. A proper chip repair is filled level, blended and lacquered, which is why it disappears and a pen does not.