Rust removal with citric acid
Got a rusty part that needs a cleanup? You can do this cheaply and easily using citric acid. Bulk purchasing from a food supply place makes this a hugely cheap way to do it. Read on for an example!
One of the bugbears of old bikes is rust, especially where you get horrible surface stuff bubbling through chrome (or on chrome). While there’s a lot of options out there, a great DIY option is to use citric acid. I recently did up the little seat mount part for the Honda C90 Supercub I dragged out of a back yard, and it came up a treat.
I don’t expect to be able to get rid of all of the rust underneath – if I do, I’m likely to eat through some of the good metal elsewhere! – but I should be able to clean it up a bit. Might end up painting the underneath matte black as a rust proofing, but the top I’d like to preserve.
I polished the top to see if there was salvageable chrome underneath, and it looked pretty ok though some pretty big rust spots were still apparent after polishing. The sides were, as you can see, terrible.
When you use citric acid as a rust reducer, go for about 50 g/L. Use hot water to make it work faster, and some washing detergent as a surfactant helps move the rust off the surface once it has been reduced back to iron.
Aim to leave the part in for about 20-30 minutes. More than that and you might get nasty pitting.
Weighing out the acid. This is from a batch of 5 kg I bought for about AU$15 from a food place online.
Acid into the hot water. 5L of water here in this tub, so 250 g of acid.
Washing up detergent as a surfactant to help.
Part in. The bubbles are actually rising up from the rust as it gets reduced. This clear solution soon…
… goes murky as the acid does its stuff. I flipped it over regularly to check out the progress.
With 30 minutes in the acid bath done, time to wash it off. A nice long rinse under some hot fresh water and you’re done. If you’re doing bare iron/steel parts then you can get surface rust pretty quickly so it’s good to treat them with oil or a wax to protect the fresh, virginal surface. Since this is chromed it should be pretty ok.
The results are nothing short of amazing.
As predicted, the inside is still a bit rusty but it is way better. The outside is nothing short of amazing.
So, there you have it: an environmentally sensitive, cheap DIY rust reducing technique that can bring new life to old parts. Properly ghetto restoration can continue.