Protecting an old car from rust is just as important as looking after its mechanical components, so if you’re becoming the owner of a classic for the first time, you should know what you’re letting yourself in for. Corrosion kills a huge number of classic vehicles.

So how much money will the long-term fight against rust cost you? It’s a complex issue, and the true cost of keeping rust under control is very difficult to pin down. Let’s look at the major considerations.

Concours vs rotten

A recently restored car should last for years without requiring welding again, if it’s been done properly. A classic car that has never been properly restored is likely to have various areas of lingering rust, which could become serious very soon (probably sooner than you’re prepared for).

There are also plenty of poorly-restored classics on the road. Most enthusiasts can give you apocryphal tales about recent rebuilds that look shiny at the point of sale, but  actually have large areas of hidden corrosion that reveals itself within a few months when dodgy filler or hastily-applied paint starts to flake away. Get to know who you’re buying from.

Compared with a ‘rust bucket’, a corrosion-free classic will cost you smaller amounts over a longer period. This makes it easier to plan your budget, and cheaper overall. But you’ll still need to spend on underseal treatment, paint touch-ups, and possibly small bits of welding or panel replacements to keep the car looking fresh.

Rust proofing

If you’re buying a car that’s in solid condition, have it professionally undersealed immediately. The application will typically cost around £500, and it should last 3-5 years. It’s vital to have this done by someone you can trust. Underseal that is applied carelessly can accelerate corrosion, not prevent it. 

Krown rust proof underseal of an Alfa Romeo 145
Alfa Romeo 145 getting an rustproofing treatment at Krown. For a small car like this their bill is around £240.

Quality products with a good reputation include those made by Fertan or Bilt Hamber. A good alternative is the oil-based treatment by Krown. Theirs is a very thorough service and competitively priced (about £250 for a small car) but you’ll need to have the coating re-applied more frequently.

Ongoing repairs

Rusty bodywork isn’t necessarily cheaper to rectify than structural corrosion. Crispy doors and panels are usually easiest to replace as a whole item, rather than welding in new metal. This can range in cost from £20 to £600 or more depending on rarity, but it’s the labour which tends to costs the most. Bills are biggest is the metal has to be sanded, filled, cut, welded, sprayed… often all of the above.

Most specialist garages need to charge at least £50+ per hour, though there are some decent blokes around who will carry out minor welding repairs for a few quid cash. Welding up an exhaust bracket, for example, is sometimes a cheap job.

Major welding jobs that require interior trim to be removed, such as renewing sills, can take a day’s labour or more.

Setting an annual budget

Preventative maintenance – stopping the rust from happening in the first place – is the best remedy, because fixing corrosion can result in bills that are much bigger than the value of the car.

It’s sensible to set aside a little money each year, because staying one step ahead of corrosion is vital to prevent it setting in. Let it build unchecked and the cost of repair can suddenly mushroom into thousands of pounds.

So come on, what’s the cost?

Let’s say you start with a solid classic car. It doesn’t need any welding yet, but it is not undersealed. Set aside about £500 in your first year for an underseal treatment, then try to put aside about £200 per year. This should cover your next rust-proofing application. With luck you’ll have some left over for paint touch-ups etc along the way.

That might sound like a lot of money, and it is. Most people don’t spend this amount so regularly, but you can bet your bottom dollar their cars suffer for it.

Here’s one final word of warning. An old car is almost always more rusty than you think it is. Get underneath and look behind the sill covers and wheel-arch liners. You’ll probably be in for a nasty surprise.

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