Wheel arch rust repair.
September 22, 2011 9:46 AM   Subscribe

How do I best repair a rusty wheel arch.

Rust has crept too far throughout the wheel arch on my Mazda. I need to stop it, but I don't have the means to cut it out and have new metal put in its place. My plan so far, is to grind and sand out the rusted areas, re-build and fill with something like 'Bondo', and then shape, sand and paint over. It might not be the prettiest of fixtures, but I'm hoping it will do. Do you have any input? What products or methods have worked for you?
posted by Frasermoo to Home & Garden (8 answers total) 2 users marked this as a favorite
Best answer: Got a picture of the spot? This is something I've been learning a lot about, but it the fix depends a lot on where the rust is. Anyway, Bondo can look great if you do it right.

Read up a bit before you start and make a plan. When you're filling a hole with Bondo, the best method is to cut out the rusted area, and dent in the area around it a bit. Then you can stick a chunk of sheet metal into the hole as a patch. Layer the bondo on top in thin layers, and then sand using increasingly fine grit until you get it smoothed out nicely.

Use proper, automotive sand paper, it lasts longer and is worth the extra price. If you're not comfortable painting, practice on a piece of sheet metal. It can be tricky, especially without a compressor, but with practice you can make it look pretty good. Most dealer colors can be matched perfectly.

Depending on how much time and effort you want to put into this, there's no reason it can't look perfect. But body work is an art, so be patient.
posted by Stagger Lee at 10:05 AM on September 22, 2011

Response by poster: Thanks Stagger. I'll get some pictures up on here in a few minutes.
posted by Frasermoo at 10:23 AM on September 22, 2011

Has it rusted all the way through? If not, you can probably get by with some POR-15 and just enough bondo to even it out before painting it. POR-15 is great stuff.
posted by pjaust at 10:32 AM on September 22, 2011

Response by poster: here are the pics. I don't think the rust has created any holes in the panel, but it has eaten away at the edges.
posted by Frasermoo at 10:43 AM on September 22, 2011

Best answer: That doesn't look too horrible. Get an electic grinder (harbor freight has some cheap ones) with sanding disks as well as grinding disks and take it down to bare, shiny metal. Hopefully it doesn't have any holes. If it does us fiberglass mesh behind the metal to give something for the bondo to adhere to. Take your time and built up slowly, sanding between layers like stagger lee says. You will have the difficulty of a compund curve around the door openings and getting that lip right. You will want to primer and paint very well to prevent the reoccurance of rust and you MUST get every speck of rust out of the metal or it will just rust under the paint.

The best way to fix this is to get a replacement panel, cut out the rusty panel and weld in the new panel and get it repainted by a professional. However this is also the most expensive, so if you are willing to let it look less than perfect you can probably do a decent DIY job on it. Check your local library for a body work how to book, and watch some youtube videos on it. With lots patience and lots of work you can get amazing results in your driveway on this kind of thing.

I see you live in Toronto and I am assuming they use salt on the roads in the winter there. Wheel arches rust out in snow country for this reason. The best way to prevent this is washing your car in the winter frequently (every non freezing chance you get) to wash of the salt. You need to pay special attention to the area in the wheel wells and underneath any plastic trim, thoroughly rinsing out these areas with a high pressure hose (like they have at DIY car washes).

Good luck and if you really mess it up It probably won't cost anymore for a body shop to fix it after you try, so you might as well go ahead.
posted by bartonlong at 11:05 AM on September 22, 2011

One idea: If you don't have a grinder, you can probably put a wire disk on a cheap electric drill to grind that off.

And yeah, it doesn't look like you should need to do any cutting.
Every thing that bartonlong said.

The good news is, that's totally not bad at rust at all. ;)
posted by Stagger Lee at 12:01 PM on September 22, 2011

Response by poster: great responses, thank you. i'm now properly motivated to tackle this. i do have a grinder, so I'll get it working.
posted by Frasermoo at 12:20 PM on September 22, 2011

If that were on my car, and I planned to fix it myself, I'd be using

1) Circular wire brush to remove all loose rust and bubbled paint, and some of the good paint

2) Thorough wetting, then Phosphoric acid rust converter treatment

3) Circular wire brush to scrub off any iron phosphate that's going to come off (any black that sticks is good black)

4) Zinc phosphate epoxy primer

5) Fine sanding

6) Bondo

7) Sanding to shape

8) If (7) exposed any metal, more primer and another fine sanding

9) Finish coats
posted by flabdablet at 11:36 PM on September 22, 2011

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