Brown paint bubbling along the lip of a rear wheel arch and a rotten sill under the driver’s door are not the same problem, even though both get called rust. The first is a bodywork blemish that every buyer in the country has seen. The second is a structural matter, and it is the one the APK, the Dutch roadworthiness test, has a view about.
The APK does not count rust or measure how much of the car is brown. It asks a narrower question: has corrosion reached a part that carries load, or that holds a safety component in place, and has it gone far enough to weaken it. Where you sit on that line decides almost everything about the sale. Our guide to selling to a car buyer covers the rest of it, including what an offer is really pricing.
What the requirement says
Take the structure first. The RDW’s APK handbook deals with the chassis frame and self-supporting bodywork in its own section, and the requirement there is that the longitudinal and transverse members may not be broken or cracked, and may not be deformed, loosened or corroded in a way that endangers their rigidity or strength.
Read that twice and notice what it does not say. It does not say rust free. It does not name a maximum patch size you can measure with a ruler. The test is whether the strength of the thing has been put at risk, and that is a judgement a trained tester makes on a car over a pit.
The same construction turns up all over the handbook wherever a part has a job to do. Axles may not be so affected by corrosion that their strength is endangered. Brake system components may not be seriously affected by corrosion. The mountings of the hinges for the doors, the bonnet and the boot lid may not be seriously affected by corrosion either.
Nowhere in any of it is there a line about a rusty wheel arch as a wheel arch. Corrosion becomes an APK matter at the moment it arrives at something that holds, carries, brakes or steers.
How the tester actually finds it
Mostly by looking, from underneath. The handbook gives the inspection method for the structure as a visual check with the car above an inspection pit or on a lift, and in case of doubt the tester reaches for a small hammer with a rounded head and for measuring instruments. Sound steel rings when it is tapped. Steel with scale behind the paint sounds dull, and when it is worse than that the hammer goes through.
Corrosion damage itself is scored in the handbook in damage units, worked out from the extent of the corrosion and from gradations published in the annexes. That machinery belongs to the tester. You cannot usefully apply it from your driveway with a torch, and no number you read on a forum is the standard. The published requirements and their annexes sit on the RDW APK handbook, and the people qualified to use them work at an APK test station.
What you can do is look in the places the tester will. Sills and their seams. The floor, the boot floor and the spare wheel well. Jacking points. Suspension mounting areas and the turrets. Brake and fuel lines where they run along the underside. Seatbelt anchorage areas. Rust that stays on an outer panel is a different conversation from rust at any of those.
What the Dutch climate does to a car
Salt, mainly. Rijkswaterstaat spreads it before the roads turn slippery, through a winter season that it runs from 1 October to 1 May, and it uses wet salt, which is moistened with brine before it leaves the spreader so that it stays where it lands. Staying where it lands is the point of it on a road surface. It is also the problem under a car, where brine creeps into seams and sits there.
Then there is the coast. Salt air reaches a long way inland in a country shaped like this one, and cars parked within sight of the water in Zeeland, along the Noord-Holland dunes or on the Wadden islands take more of it than cars in Utrecht. Add a car that only does short trips, so the underside never gets warm enough to dry, and you have the local recipe.
None of that is a defence for a seller. It does explain why an older Dutch car so often has rust at the back of the sills, and why a buyer here is rarely shocked by it.
What a buyer does with it
A trade buyer looks where the tester looks, because the tester’s verdict is what the car is heading towards. A private buyer with a torch does roughly the same thing with less confidence. Both of them look for one extra thing, which is whether somebody has painted over it.
Underseal sprayed on last month over scale is visible, and it reads as concealment whether you meant it that way or not. It converts a conversation about a rusty car into a conversation about a seller who tried something. Describe the rust, photograph it, say where it is and say how long you have known.
The record has a part in this too. The APK history with its repair and advice points shows up in the free RDW vehicle report, which an owner can request with DigiD, and the RDW asks a seller to hand the buyer the report of the last inspection. An advice point about corrosion from two years ago is therefore already in writing, and the buyer may well read it before you mention it.
Treating it, or selling the car as it is
Our answer on treatment is no, and we would prefer you did not. Surface rust tidied up with a wire brush and a rattle can is cosmetic work that nobody is fooled by, and structural corrosion is a welding job followed by another inspection, on a car you have decided to part with.
There is a harder version of this that is worth saying out loud. Where a car fails on corrosion in a load bearing member, the welding needed to put it right is often more than the car is going to be worth afterwards, and that is the point at which many owners stop spending. The choice in front of you is a bodyshop estimate held against an offer for the car in its present state.
If the rust is honestly cosmetic, leave it alone and describe it. If it is structural, the car is still saleable, and an expired or failed APK does not stop a transfer either. A car that should not be driven goes onto a transporter and never moves under its own power.
When you want a figure for the car as it is, ask us for an offer, and put the rust in the request: where it is, how large, whether it has been through an APK with it. A number plate (kenteken) and the mileage are enough to start, photographs help, and how soon the offer comes back depends on how much detail came with the request.
Frequently asked questions
Does rust make a car fail its APK?
Only where it has reached something structural or safety related and gone far enough to matter. The handbook requirement for the chassis members and self-supporting bodywork is that corrosion must not endanger their rigidity or strength, and similar wording covers axles, brake components and hinge mountings. Rust on an outer panel is not covered by those requirements.
Is a rusty wheel arch worth repairing before I sell?
As a repair for the sale, no. Paint and filler on an arch do not change what a tester finds underneath, and a buyer prices the car on what is there. We do not ask anyone to repair or clean a car before we collect it.
How can I tell whether my rust is structural?
Look from underneath at the sills, floor, jacking points and suspension mountings, and compare that with rust that sits on a wing or a door skin. Where you cannot tell, an APK test station can, and the handbook requirements and their annexes are published by the RDW.
Will the buyer find out about old corrosion anyway?
Probably. Repair points and advice points from past inspections appear in the APK history in the RDW vehicle report, and the RDW asks you to give the buyer the last inspection report.
Can you buy a car that has rusted through underneath?
Yes, including one that has failed an inspection on it. Tell us where the corrosion is and let the offer reflect it. Collection is free anywhere in the Netherlands and the whole sale runs in English.