Michael Fernie profile picture Michael Fernie 4 years ago 67
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The 5 Worst Aspects Of Repairing Rust

Rust repair is about as tedious as working on cars can get, but it could save your car from the crusher

Remind me later
The 5 Worst Aspects Of Repairing Rust - Blog

If you’re not careful, rust can be a complete car killer; let it get too far and your once beloved daily driver can swiftly become a resident of the local scrapheap. Creeping its way through every crevice in a car’s bodywork, any area of water accumulation will begin to eat its way into your car’s once solid bodywork, turning it into an ugly tan mush.

So when those dreaded bubbles start emerging through your sills and wheel arches, it’s time to take a deep breath, man the angle grinder and save your vehicle from the grip of corrosion.

Rust repair is the colonoscopy of car restoration - you try to forget about it, but you know some day you’re just going to have to knuckle-down and get it over with. So you won’t find many amateur mechanics who have had a fun day of rust repairing in their driveway. And having just performed a clean-up of my MkII MX-5’s sills and wheel arches, here is a list of the worst things you will encounter when performing the much-needed automotive surgery.

It's always worse than it looks

The 5 Worst Aspects Of Repairing Rust - Blog

From the outside panel, the rust may seem like it’s just a small patch that has managed to get a hold on the extremities of your bodywork. However, once you begin the process of sanding back the surrounding paint (and possibly old filler) you will soon realise that rust always manages to migrate to a much wider range of surrounding bodywork, with the bit you can see as the epicentre.

With the MX-5 – and many other convertibles – the problem is they rust from the inside-out. This is due to drainage holes for the roof clogging up, sending torrents of rain water cascading into the sills and rear wheel arches where it sits and eats away at the inner structure of the car. So after taking the angle grinder to the wheel arch, the outer skin is stripped off to reveal a corroded inner sill.

Instead of a quick cut and weld job, it suddenly becomes a full clear-up of the inner structure of the car which will need welding to provide a decent support for the outer bodywork.

Hesitation and the love for your car will hold you back

The 5 Worst Aspects Of Repairing Rust - Blog

Unfortunately, you have to be a full-on savage when it comes to cutting any piece of corroded metal out of the area you are trying to repair. Before welding begins, any metal that has been kissed by the poisonous lips of corrosion has to be plunged into by the angle grinder as only clean, bare metal can be used for efficient welding to take place.

This can be extremely heart-breaking, especially when at one point your car is left with gaping holes in its bodywork that initially seem beyond repair. But things have to get worse before they get better with this kind of repair, so you just have to suck it up and be willing to see lumps of semi-corroded metal lying on the ground.

Previous bodged rust repairs will ruin your life

You can see the white filler has been sanded back to an extent, exposing huge gaping holes
You can see the white filler has been sanded back to an extent, exposing huge gaping holes

I don’t know what crosses people’s minds when they decide that entire sheets of metal can be replaced by white, gummy filler, but you’ll be surprised how many ‘restorers’ will take this easy route. Plugging rusty holes with filler is a quick fix but in the long run, the filler will either soak up water that would otherwise run off the car, feeding it back into the bodywork, or it will not provide any significant form of protection and will let water and moisture seep through from the surroundings into places you really don’t want it to be.

Sanding the bodywork back on the Mazda showed that the metal was heavily corroded and held together with half-inch thick filler which – once sanded – covered the entire driveway in a film of white particles. It is the equivalent of filling a hole in your favourite jeans with blue tac and makes the initial sanding process a complete nightmare. Just don’t. If you’re going to do it, do it right.

Replacement panels can be cheaply built and don’t quite fit

The newly repaired (and slightly skewed) sill and wheel arch ready for painting
The newly repaired (and slightly skewed) sill and wheel arch ready for painting

If you’re lucky, you’ll be working on a car that is popular with amateur mechanics and has reproduction parts readily available. In the case of cars that have popular rust spots that become synonymous with that particular car, someone somewhere will manufacture complete replacement panels to replace the rusted ones.

Unfortunately, they’re never going to be to the standard of the original body panels and often get easily bent in transit from the engineering firm. So once the supportive metal has been welded underneath, it’s a frequent occurrence that you’ll go to line up the outer panel ready to weld it on and it will seem like it doesn’t fit at all.

The clean metal is now ready to have the outer wheel arch welded on, but it rarely fits exactly
The clean metal is now ready to have the outer wheel arch welded on, but it rarely fits exactly

So suddenly what you thought would be a simple jigsaw piece missing from the puzzle becomes this awkward sheet of failure that needs constant tinkering through bending and cutting to make sure it’s a snug fit.

Because one of my replacement wheel arches was so far out, the passenger side of my Miata now splays out slightly from the rest of the car. Only the geekiest of MX-5 experts would ever realise, but the fact I know it’s there and I bought it thinking it would be an exact swap makes me toss and turn at night.

Your car will look like s**t for weeks

All welded up and ready for daily use. Surface rusts appears surprisingly quickly, but it is easily sanded back before painting occurs
All welded up and ready for daily use. Surface rusts appears surprisingly quickly, but it is easily sanded back before painting occurs

If you work a normal week, it probably means that the weekends are the only time to work properly on your car. Depending on what area of your car needs repairing, the work can take a good few weekends before it is all ready for the paint shop. This repair here has taken me around 10 hours per side which equates to around a month of weekends.

As I use the MkII as my daily, this means that I’m performing a rolling restoration, which opens the poor MX-5 up to some serious criticism when I turn up at university or events. Gaping holes, bare sheet melting merging into painted areas and the odd skim of surface rust cover the areas you’ve been working on and don’t make your car look the prettiest. It would be like getting plastic surgery on your own face but only in small segments at a time. You’d look a bit wonky and scarred for the first few times but in the end you’ll turn out looking gorgeous. So hold tight, it’ll all be worth it in the end.

Goals...
Goals...

Rust repair is definitely something that every keen petrolhead should try at some point in their lives. Obviously it would be preferable to start with something cheap like I have, but in the long run it could be training for when you have to save something much more special and expensive. So my advice would be to remember it’s never too early to start a rust repair, nor is it too late. If your car has a flew rust rashes here and there, get on them now before they become dangers to the structural integrity or the car.

At the same time, every car should be worth saving, and rust repair - although time-consuming - can be an extremely rewarding process that could keep one more interesting and rare car on the road. So, what are you waiting for?

Have you had any rust nightmares? Share your woes below!