pstock

how should I proceed in treating this rust?
this is one the chain stay of a Bike Friday Tikit, which I believe is a solid tube (it is pretty small OD)
I am not overly concerned about cosmetics - this is a working bike. so a bit of off colour touchup paint is not the end of the world.
Sand it?
then.... would I prime it before touching up?
if so, is there special bike frame primer I would use?

unterhausen

I am not sure it's a solid rod, I think it's a tube.

With rust that bad I would probably use evaporust.

pstock

Evporust I have.
and after that?

Andrew R Stewart 

After that... ride the bike, keep it clean and waxed. Andy

unterhausen

I think I would get some rustoleum and paint it after the evaporust. I am not sure what's going to happen to the rust under the paint, I think you just need to keep up with it better this time.

Andrew R Stewart 

Peter- What you do is entirely dependent on what you expect and will settle for, and I don't want to start a patina VS showroom tangent (leave that form the CR list) but here's some thoughts.

I would remove the loose but not yet flaked off paint mechanically. Sand, wire brush, back edge of hacksaw blade. This will also remove the loose rust. Soak in Evaporust. Prep for paint (I would sand off the vast majority of the Evaporust on the unpitted areas but by soaking even the pits will now have been treated). Paint, brush on or spray I would use a rust inhibiting primer.

How's the rest of the bike's finish? BFs tend to get beat up and often spend time wet. One of the earlier ones that I have dealt with was when I lived in Cleveland, OH. With the road salt mine just off shore a few miles the local highway depts spread it around like sand in the Sahara. This BF ended up with one of the hardest to remove BB's I have seen... This bike had a lot of rust fingers running away from the various bosses, faces and hinges. It ended up being stolen when my customer was vacating in FL and before he returned home he had ordered the replacement (and I did some winterizing assembly steps that the first hadn't seen). I always thought these bikes didn't get the props they deserve. They are an interesting frame to paint with the ability to separate the different frame sections. I wonder if one could get decals... Andy

Doug Fattic 

Because I am a painter, I have the perfect tool to eliminate rust and that is a sandblaster. That gets everything down in the deepest pits. I try to smooth the surface some afterwards with a emery (and maybe a fine toothed file). Then I am ready to put on epoxy primer. If I want the paint to look smooth when finished (instead of pitted), I fill the pits with spot putty that is sanded smooth before applying top coats. If there are deep pits it might take several applications.

mrv 

This PERMATEX stuff makes me feel like I'm doing something for exposed or rusted metal. It's brushed on and dries to kind of a purple-black. It stains existing paint,but it sound liked the OP didn't care about cosmetics, just wanted to stop the termites from spreading, so to speak. I would recommend only using it like you would a touch up paint. It's a total P.i.A. to remove if put over large portions of the frame. Seems like it really gums up sandpaper. (I can point to a post I ranted about it if more info - or a good laugh - is needed.)

https://www.permatex.com/products/sp...reatment-8-oz/

I would be curious to know what the folks who make a living at frame finishing think of it.

Thanks.

zandoval 

WOW... You'se guys are suggesting some pretty fancy treatments but I'll chime in. I would hit it with a Bastard File and a Wire Brush to get ALL of the rust off. I would then try to sand out any remaining pits. I would then after manually getting all the rust off, coat the area with Vinegar, and let it sit for a day. I would then paint it with a brush on Rustolium enamel after an using an etching rattle can primer.

When I take on rust as you have pictured I go whole hog. I took on an UO-8 from Galveston once. Rust was extensive but luckily the inside of the frame had been treated with Linseed Oil. On a few of the pits I had to use Bondo to smooth out the surface before painting.

There are a lot of good things to be said of Chemically removing rust but I use BRUTE FORCE...

mrv 

Related to the OP

How deep of pitting is too deep to consider spending time & money on a frameset?

This is an 86 Allez Specialized
I’d like to refinish it. Probably a DupliColor metal flake cobalt. Get a nice Tri Color Shimano groupo

https://cimg3.ibsrv.net/gimg/bikefor...45d6282c3.jpeg

JohnDThompson 

Paint the bare area with linseed oil. If/when rust reappears, take it off with steel wool and re-apply linseed oil.

unterhausen

It seems like heating the frame a little before applying the linseed oil works pretty well. You can even get it hot enough to make it black. I have a frame treated with linseed oil that hasn't rusted yet. It has only been in my garage though.