I neglected one of my bikes, and it’s been sitting under a layer of mud and rotted pine needles for 3 years. I’ve given it a quick wash, and some of the paint has come away, leaving white and bumpy aluminium. It’s worst on the chainstays behind the bottom bracket, and on the underside of the canti bridge & seat stay joins. I took it to a bike shop, but although they seemed interested and intrigued, they weren’t able to offer any advice or help. It’s likely the frame is scrap, but I wouldn’t mind seeing if there’s a way to fix it up/prevent further corrosion, and knowing what sort of place could do the work.

Aluminium oxidises into a protective layer usually. Though these are alloys of aluminium but generally does the same. It shouldn’t corrode destructively I think, though maybe some funny stuff can go on with some alloys. I know aly frames apparently degrade over time anyway.

That said, the mud may have eaten away at it a bit if there was something corrosive in it.

Could be you could just get it all polished up or raw the frame and paint or lacquer.

Rub it off – primer & paint/laquer. Good as new.

Thanks. I read something about aluminium not oxidising if it was starved of oxygen, which it possibly was under the dirt. I think I noticed some white deposits on top of the dirt before I washed the bike.

Check you can strip the parts, seatpost and BB, before spending any time on it.

If you remove the protective layers (paint then oxide), the aluminium can corrode happily. Composting pine needles ought to do the job nicely because they produce a range of organic acids

Yes, every time I see the bike I mean to check the seatpost hasn’t seized!

dpfr, does that mean the frame might be ruined?

I’ll maybe take it to a car restorer and see what he reckons. If it’s structurally okay I’ll look into having it repaired or resprayed.

I’ve not seen one that was structurally iffy, but I have seen frames where the cable stops fall off etc after corrosion.

Depends entirely how thick the metal is and how badly corroded. It could just be surface corrosion (gritty feel to the surface and stuff rubbing off easily) or it could have pitted more deeply. You might be able to see if you remove the corroded layer and take it down to bare metal. If it has only been a couple of years, I think it would probably be OK but you need to get someone who knows what they are doing to take a look.

If you find a local company that powder coats bike frames, they should have acid dipping tanks for cleaning alloy parts. If you are looking for a professional re-finish, you could ask them to strip it, then inspect it to see if it’s worth saving it, if any pitting is deep they may not want to re-coat it for you anyway.

If there is nothing obviously terrible then just make a note of where the bad areas are, clean them up with fine wet and dry and ride it till it breaks (at your risk just to absolve myself of any blame).

Pitting can lead to cracking eventually but i’m not sure I would be too worried as it doesnt sound like your main bike that you take on DH runs.