Rust creeping under paint - what to do?


New member
I'm Thorsten from Germany. I'm new to this forum ... and in need for a little help.

Sitting in my basement is Yo Eddy No. 131Y3M, which has shown me a some true kandy wildcherry times over the years. For several reasons though it has been out of the woods for a while now.

When I was checking on the frame recently I discovered it obviously has developed some rust problems. Not the usual drama, the seat tube is fine. The Yo has rust under the paint.
The main affected areas are seat- & chainstays. The rust seems to be spreading from small chips in the paint job. From there it is creeping under the paint and forms what looks like small veins.
I did some prodding with a screwdriver. There is rust underneath, but it all seems to be fairly superficial. However, I'm not sure what to do now, and I hope you guys can give me some advice on this.

From your experience: How dangerous is that kind of rust? Will it remain superficial or will it eat holes into the frame in no time? Do I have to take quick & radical action (glass blasting, stuff like that), or will mild measures be enough to stop it?
I read about phosphoric acid being able to convert rust. Would such a treatment prevent the rust from spreading and/or eating deeper into the steel?

Problem is this: I love that Yo and want to bring it back to life again, but at the moment I'm short on resources. Things like a repaint are definitely out of range for the time being. So basically, I'm looking for a buckshave way to save my Eddy. Apart from *gulp* selling it. Any ideas?



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Ronin 09

New member
Personally, if you can't afford to respray it now, I would sand back the affected areas to bare metal, give them a dose of kill rust, then spray automotive primer/surfacer over that area to seal it off.

then when you have more time/resources, get it repainted.

I wouldn't leave mine that way - as you don't know how bad / superficia the rust is under paint.

my 2c


New member
Thanks for the replys guys.

Ronin, I thought about something like that also, but that would mean I'd definitely have to respray it then. I was kind of hoping there was a way to stop the rust and keep the original paint .

Helmut, I've been a lurker on that forum for quite some time and did searches there as well but couldn't find anything on the kind of rust on my Yo.

I just found out a little more about the type of rust: It is called filiform corrosion or underfilm corrosion. Here's some info, even with a little movie:

If I get that right, the process is largely superficial. Corrosion seems to take place only in the head of the filaments, the 'tails' are said to be 'inactive'. That kind of confuses me, I thought there was no such thing as 'inactive rust'. Any metal experts around to confirm / clarify that?
And I couldn't really find anything on how best to deal with it. If the tails really are 'inactive', could exposing them to more air by opening the filaments up be counter-productive?
The prevention tip on that one site seemed even more confusing - 'use brittle coatings', I thought brittle/chipped coating is a condition to start the process in the first place.
Questions upon questions ...


New member
I have a 94 Yo in aquafade - same story. It's been there for years and doesn't seem to get any worse. Annoying though...

Dr S

New member
Thats nonsense. I run a company here in the UK that deals with corrosion issues on classic cars. Iron Oxide will continue its chemical reaction in all directions- it has no sense of direction. It will be many many years granted until it eats its was inwards but if I were you I would try and get it proffesionaly repainted sooner rather than later. Until then spray it regularly with a good corrosion inhibitor such as PX24 to slow the process. it won't do it any harm to be cautious.



New member
Thanks for the input DrS. That's exactly the reason I was posting it here, to get decent assessments. I'd rather be overcautious about this than ruin the Eddy. The idea of 'inactive rust' sounded suspicious to me from the start.
From what I've read by now it seems my basement may have a humidity problem, as this type of rust allegedly needs 60-95% humidity to grow. So for the time being, first thing I'll do is store the frame in a different place and shorten the oil coating intervals. Then I'll get a converter / inhibitor and treat the rust.
If anybody got any further ideas or knowledge to share, don't hesitate.


New member
Hey Gang

Another possibility is that the frame was painted during high humidity conditions and occult moisture was present on the surface when the frame was sprayed. We did not have sophisticated paint boothes that were climate controlled. Often during the summer months, the painters would work at night when the conditions were more favorable.

On a good note, the seatstays and chainstays are sealed so the probability of rust forming from the inside out is extremely low. Keep in mind that the YO seatstays are only 0.028" thick so keep an eye on the spreading.

I don't have any easy solution for the problem. It seems that stripping and respraying would be the only permanent solution.

Good luck
Scott Bengtson