Guides
How to Inspect Bodywork and Rust on a Used Car
How to Inspect Bodywork and Rust on a Used Car
Summary:
- The most rust-prone spots are the door sills, wheel arches, chassis rails, and boot floor — always check them with a torch.
- A magnetic paint thickness gauge reveals filler layers invisible to the naked eye: readings above 200 microns indicate significant repairs.
- Signs of repainting — overspray on rubber seals, misaligned panel gaps, uneven texture — betray undisclosed accident history.
When you buy a used car, you're trusting what you can't fully see. The bodywork is the first thing you notice, but it's also the easiest thing to hide. A fresh coat of paint can cover dents, filler, and even structural damage, turning a car with a troubled past into something that looks immaculate. But for those who know where to look, the clues are almost always there. This guide walks you through a systematic inspection — what to check, how to interpret thickness gauge readings, and when to walk away. Before you finalise any deal on CarPulse, spending thirty minutes on this check can save you thousands.
Why bodywork matters when buying used
Mechanical parts can be repaired; a compromised body shell never fully returns to its original state. An engine needing a rebuild has a predictable cost; bodywork with structural rust or a bent chassis can make a car dangerous or economically unrepairable. Italian body shops estimate that repairing a rusted wheel arch costs €300–700 per side; restoring a deformed chassis rail can exceed €2,000, with the car off the road for weeks.
In the used car market — especially under €10,000 — vehicles with undisclosed minor accident damage or evolving rust are common. Learning to recognise them takes method and about thirty minutes. Before you assess the mechanics, the bodywork tells you whether the car has had a quiet life or has something to hide.
Critical inspection areas
Not all parts of a car rust at the same rate. Water collects in specific places, and those are where you look first.
Door sills (sottoporta): The horizontal beams running beneath the doors, between the wheels. They're easy to overlook. Crouch down and shine a torch along them: look for paint bubbles, rusty chips, or metal that sounds hollow when tapped. Through-rust here means expensive repair and loss of structural rigidity.
Wheel arches: Constantly bombarded by stones, mud, and water. Push the plastic liners aside gently and look underneath. Surface rust on the arch lip is common; rust on the inner wing panel or surrounding shell is more serious.
Chassis rails and cross-members: The backbone of the car. Get underneath on a level surface with good lighting and check the longitudinal rails along the floor. Any dents, straightening marks, or unusual welds indicate a significant undisclosed accident.
Boot floor and spare wheel well: Lift the carpet. Rust, moisture, or a musty smell indicate water ingress — often the sign of a poor repair after a rear impact.
Door edges and A/B pillars: Open all doors fully and inspect the inner edge. Paint chips here first, and rust advances from the inside out. Also check the base of the A-pillars (windscreen pillars), where moisture tends to collect.
Reading the paint: signs of repainting and accident damage
A repaint isn't automatically a dealbreaker — it may have been done after a properly repaired minor scrape. The problem is when it's been done to hide something. Here's how to tell:
Colour mismatch: Compare panels at the same light angle. Even subtle tone differences — a bonnet slightly darker than the wing — mean a panel was resprayed independently. View from behind the car towards the light source, not head-on.
Overspray on rubber seals: Run your finger along the rubber seals around doors, the windscreen, and the rear window. Feeling paint granules means the adjacent panel was sprayed without properly removing the seals — a quick, low-quality job.
Overspray on glass: Look at the edge of any window from outside: a fine grainy haze indicates paint sprayed without adequate masking.
Orange-peel texture differences: Uneven texture like orange skin is normal on many factory finishes. But if the texture differs noticeably between panels — one unusually smooth, another unusually rough — the anomalous panel has likely been resprayed.
Panel gap alignment: Open the bonnet and all doors, and check that the gaps between panels are even along their full length. Variations of even 1–2 mm suggest a panel has been removed, deformed, and refitted, or replaced entirely.
The paint thickness gauge: how it works and what the numbers mean
A paint thickness gauge measures the depth of paint applied over metal. It uses magnetic induction: press it against the panel and it gives a reading in microns within seconds. Entry-level models cost €20–50 and are perfectly adequate for a purchase inspection.
Reference values:
- 80–130 microns: Typical factory finish. The panel has never been touched.
- 130–200 microns: Grey zone. Could indicate a light respray or just production variation. Investigate further with other checks.
- Over 200 microns: Almost certainly filler or primer has been applied in significant quantity. The panel has had bodywork repairs. The higher the reading, the more invasive the repair.
- Zero or inconsistent readings: May indicate aluminium or plastic panels (where magnetic gauges don't work), or heavily layered damage.
How to measure correctly: Take at least 5–6 readings per panel at different points. Always compare matching panels (left wing vs right, front door vs rear door on the same side). A difference of more than 50 microns between two identical panels warrants attention.
Find listings with documented history and verified mileage on CarPulse used car search, where you can filter by condition and service history.
Types of rust: surface oxidation, structural rust, and paint bubbles
Not all rust is created equal. Understanding which type you're looking at changes the risk assessment entirely.
Surface oxidation: Orange or brown spots on exposed surfaces, often on cut edges during production. If the underlying metal is sound, this is a cosmetic issue treatable with rust converter and paint. Common on cars over ten years old.
Through-rust (structural): Rust that has eaten completely through the metal, creating holes or zones where the panel gives under pressure. On door sills, chassis rails, or the floor pan, this is unacceptable: it compromises shell rigidity and crash safety. A car with structural rust in these areas won't pass its next roadworthiness test.
Paint bubbles: Raised blisters under the paint, often on panel edges or in corners. This means rust has already started beneath the surface and is expanding invisibly. Scratch gently with a fingernail and the paint gives way to reveal oxidation underneath.
Signs of previous accident damage
Beyond rust, a car may have sustained accident damage that altered its structure. The most reliable indicators:
Ripple lines in panels: Under raking light, a poorly straightened panel shows subtle waves. Use the sun or a side-held torch at the lowest possible angle to illuminate panels obliquely.
Fresh undercoat in isolated spots: Open the bonnet and look for patches of very fresh grey or white primer, localised to one area. A recently resprayed spot in a corner of the engine bay is suspicious.
New bolts or clips on aged panels: Bright, unoxidised screws surrounded by years of grime mean that panel was recently removed and refitted — a strong sign of post-accident replacement.
Unusual or excess welds: Every car has its factory welds, regular and continuous. Extra spot welds, irregular joins, or excess underseal in isolated areas indicate post-accident work on the shell.
If in doubt, the best protection is an independent mechanic's inspection. You can also use CarPulse Valuation to compare the asking price against market values and gauge negotiation room.
FAQ
Do I really need a paint thickness gauge, or can I skip it?
It's not mandatory, but it's strongly recommended. The human eye can't perceive thickness differences below a millimetre, while a €30 gauge reveals filler layers that are invisible. On any car over €5,000, it pays for itself the first time it helps you avoid a bad purchase. Alternatively, bring a trusted mechanic or body shop professional.
Is surface rust a dealbreaker?
Not necessarily. Small oxidation spots on edges or the underside are normal on cars over ten years old. The problem arises when rust is through the metal, when it's located on the door sills or chassis rails, or when paint bubbles indicate it's progressing invisibly. In those cases, negotiate a discount to cover treatment costs — or walk away.
What does overspray on rubber seals actually mean?
It means the adjacent panel was painted without properly removing the seals — a hallmark of fast, cheap bodywork. It doesn't necessarily indicate severe structural damage, but it does mean the repair quality was low, and often that something was being hidden quickly. Always follow up with a thickness gauge reading and check the accident history.
When is a professional inspection worth getting?
Always, for cars above €8,000–10,000, or whenever you've found suspicious signs but aren't sure of their severity. An independent mechanic's inspection costs €50–150 and can reveal mechanical and structural issues that a visual check misses. If the seller refuses to allow an inspection, treat that refusal itself as a warning sign.
Conclusion: an hour of checks beats months of regret
Inspecting bodywork and rust before buying a used car doesn't require engineering expertise — it requires method, a torch, and the willingness to look where others don't bother. A thorough checklist, combined with a thickness gauge and a history check, gives you solid protection against the most common risks in the used market. If something feels off, don't be rushed: good cars don't run out. Browse the CarPulse catalogue with advanced filters to find the right vehicle, with the history you deserve to know.