I think I may have a trace of rust...

[Ming the Merciless]

That's amazing! It's even changed the shape of the tap!

Put it on an old steel bike frame and a new lightweight aero carbon frame comes out the process.

 

[C R]

Would this be any good?
https://ebay.io/m/oCb3Ge

 

[wafter]

Oxalic acid doesnt harm the good metal -or paint - in the slightest.

I think all acids will attack the metal to an extent - it's just a case of how long this takes based on how strong they are; and hence how much margin of error you have before it becomes problematic.

Would that be good as a post-acid treatment? And presumably for the less serious frame rust elsewhere. I'd prefer the least aggressive route that will actually work. Would this survive the daily rough 'n tumble, or might it just wash off? In which case, I don't know, some kind of varnish? Any thoughts appreciated.

I'm not sure - if you're removing the rust I think you want as robust-a-finish as possible; i.e. a decent paint but this brings us back to the practical issues of prep and application in my last post. I think really it needs to be one of two extremes - remove all corrosion and fully refinish the frame (or at least the affected area) to a high standard (which has always been difficult; probably harder still now with environmental regs on consumer paints) or impregnate the rust with something that's going to stop it getting worse.

I'd caution against WD40 as over time the solvent evaporates off and leaves a tough, sticky residue that you probably don't want in your seatpost tube.

FWIW I've apparently had success applying a softened wax to the latch on my garden gate - the galvanising on which had failed allowing surface rust to develop; however left in the sun the wax has melted, wicked into the rusty surface and now appears stable..

Since the frame's clearly never going to be a minter (and being a working bike there's an arguable benefit to leaving it looking tatty) I'd be more inclined to largely leave the rust as-is and try to take measures to prevent it getting worse. That said if you do treat it with an oil / wax preservative that will limit you to mechanical rust removal in future as it will prevent chemical treatments from working.

 

[Drago]

Im a physics man rather than a chemistry type geezer, but my limited understanding is that oxalic acid chemically reacts with oxides, so clean metal is left alone. Certainly in my personal experience it has never visibly etched clean steel or caused even the slightest visible damage to paint.

 

[Brandane]

And spraying WD-40 into all the tubing sounds like a really good idea.

If you're serious about spraying into the tubing, I would suggest that you follow (motor)bikers example and use ACF50 rather than WD40. It is far more durable, and better at rust prevention too!

Motorcycle | ACF-50 https://share.google/jkP2YARt9asTlPqRr

 

[Drago]

Buzzweld ACE is better still.

 

[swee'pea99]

Would this be any good?
https://ebay.io/m/oCb3Ge

Thanks, I did spot that on my searches, but, sad as it sounds, I baulked at the nine quid for a lot more than I'll ever need when I was after a couple of quid's worth of basic powder. I like basic powders that do basic things well. Hence the citric acid under the sink, which, thanks to AI I now find I can use - and how to do it:

Excellent! I shall give that a go and report back. As for the afters, again, while I'd like to protect the bike from future actual damage/corrosion, I don't think I need anything too extreme. The WD40 strikes me as a good cheap & cheerful solution for the tube interiors. If the solvent evaporates and leaves a sticky residue, that sounds fine to me. It's a barrier. Which, let's face it, is more than it's had for the last 50+ years. The outside, I'm not so sure. Again, I hate to sound cheap (I am) but ACE and Buzzweld, though I'm sure they're great, feel a bit like overkill for a tatty frame which has come through fifty+ years of neglect commendably unscathed, and will hopefully be good for 50 years more with just a little TLC. Even just decent car wax maybe? I don't know. But many thanks for all suggestions - all excellent grist to the mill!

Anyway, that's for tomorrow. I have paste to make!

 

[Moon bunny]

I hear boiled linseed oil is favoured for "sympathetic" protection but I've not tried it.

Not nowadays, vegetable oils have been found to turn acidic and attack the metal they were supposed to preserve.
Tannic acid, found in various proprietary products (no need to brew up), well washed off, followed by Renaissance wax is the museum standard.

 

[Fastpedaller]

Im a physics man rather than a chemistry type geezer, but my limited understanding is that oxalic acid chemically reacts with oxides, so clean metal is left alone. Certainly in my personal experience it has never visibly etched clean steel or caused even the slightest visible damage to paint.

I'm in agreement. It seems there can be 2 approaches (is that the correct word?) to rust - rust removal and rust conversion. I've used both over the years, and both work but it does indeed depend on what subsequent coating are applied. If not using paint (ie putting heavy wax /oil over I'd suggest rust conversion (oxalic acid) or similar would be best - only my opinion though

 

[wafter]

Not nowadays, vegetable oils have been found to turn acidic and attack the metal they were supposed to preserve.
Tannic acid, found in various proprietary products (no need to brew up), well washed off, followed by Renaissance wax is the museum standard.

Thanks - didn't know that!

 

[swee'pea99]

Well, so far so good!

Made up a 10% solution of citric acid (5ml, in 50ml of water - the smallest amount I reckoned I could make with any confidence in the ratio), then mixed it into a ceral spoon of plain flour. Didn't form a paste; more like a pizza dough - stretchy and clingy. Which proved excellent for applying, making it easy to work it into all nooks and crannies, using a toothbrush.

Added a bit of cling film, left it a couple of hours and rinsed off and....

I'm quite pleased with that! Leave it to get bone dry, remove the bubbled paint, then...I'm thinking maybe car wax....but no. Apparently this is a poor idea:

Rust-converter. Oo-er. This is all more complicated than I imagined. Oh well, that does sound like something really does need attending to. Off to find some rust converter...