Short answer: surface bloom on bare metal is cosmetic and is dealt with from 5,000 CZK. Bubbles under the paint mean corrosion is working from underneath and the metal has to be opened up. A rusted-through sill or structural part is a defect that will fail the technical inspection.
Three stages of corrosion
| Stage | What it looks like | What's needed | Indicative price |
|---|---|---|---|
| Surface bloom | A film of rust on unpainted metal; the panel is still solid | Cleaning, treatment, protective coating | from 5,000 CZK |
| Bubbles under the paint | Blisters and lifting paint that cracks when pressed | Opening up, cutting out the affected area, paint | from 8,000 CZK |
| Rusted-through metal | A hole, soft metal, a rusted-through sill or edge | Cutting out and welding in new metal | from 3,000 CZK (depends on the extent) |
Why rust comes back after a repaint
Corrosion doesn't work from the surface inwards but most often from the inside out — from cavities, from welds and from places where water sits. If a rusty area is simply sanded and sprayed over, the metal under the new paint keeps corroding and the same bubbles appear within months. That's why we open the affected area down to sound metal and address cavity protection too, not just the visible surface.
Where corrosion appears most often
- lower door edges and sills — salt and water trapped inside
- wheel arch lips — stone impact
- around the windscreen and rear screen — leaking bonding
- areas from poor previous repairs where metal was left badly treated
- the underbody and wheel wells on cars used all year round
Rust and the technical inspection
Corrosion on a cosmetic panel is not in itself grounds for failure. The problem starts when a structural element is compromised — a sill, the floor, suspension or seat-belt mountings. Such a car is judged unroadworthy. If you're unsure whether your area is cosmetic or structural, send a photo — we can tell from it.
Is rust repair worth it on an older car
On a car you plan to keep driving, acting early almost always pays: an area that can be handled locally today is a major welding job in two years. On a car you're selling, what matters is whether the rust is on a cosmetic panel or has reached a structural part. We'll say plainly when the money won't come back.
Frequently asked questions
Will a car with rust pass the technical inspection?
If the corrosion is only on a cosmetic panel and the structure is sound, usually yes. A compromised sill, floor or suspension mounting is a defect that will fail the car.
Why does rust come back even after a repair?
If the rusty area is only sanded and repainted, the metal under the paint keeps corroding. The affected material has to be opened up to sound metal and the cavity it comes from treated as well.
Can a rusted-through sill be welded?
Yes, the rusted section is cut out and new metal welded in. We can only state the extent once it's opened up — photos show the surface, not how much material is affected underneath.
What does rust repair cost?
From 5,000 CZK for a small spot, from 8,000 CZK for a larger panel area. Welding in and replacing a rotten section starts at 3,000 CZK — the final price follows the extent, which only shows once the area is opened.
Can corrosion be slowed without repair?
Cavity and underbody preservation slows new spots from forming, but it won't stop what's already working under the paint. An existing spot has to be dealt with.
What to do now
Photograph the area close up and the whole panel, ideally in daylight. Tell us the car's age and whether it's parked outside. From the photos we'll say which stage the corrosion is at and what scope of repair to expect.
