I had a steel frame repainted about 5 years ago. The painter sandblasted it and used oven cured paint. Some rust spots appeared on the TT and BB underside, the paint peeled off. I asked the painter about that and he said that once rust has formed, it always appears again after a long time, maybe years, no matter how well you clean it - sandblasting, acid, polishing. Is this true or just an excuse?

Depends on the rust --- and depends on the surface preparation before paint

if you merely touch a freshly sandblasted piece of metal , you can see a rusty fingerprint in a few days ---

--- The car guys seem to do ok -- and that's with thin sheetmetal ---- serious rust you cut out and patch -- surface rust you sane/blast off, -- clean , prime, and paint

If the rust was pitted and nasty though, -- perhaps some was not able to be removed ---- sometimes there is rust between the lug and the tube that takes years to propagate and there's nothing that can be done about it though, --

I am with DMC- depends where it is and where it is hiding. the painter maybe could have done a better job... but its hard to say. rust sucks.

I used Brownell's Oxpho Blue cold bluing liquid to treat rust on some older neglected firearms. It seemed to work for at least 20 years, particularly in hard to reach crevices and places that could not be disassembled. I've also used it on old tools and other steel items.

It's worth a try on steel bike frames, especially in crevices.

chemically/physically, that would make no sense.
In real life, if there starts rust to form in certain areas, it is for a reason - BB underside is sandblasted by road dirt, TT is thigh rubbing zone and sweat-sprayed. If you don't address that reason, new rust will start to form on the same spot. But it isn't because rust was there before.

If the bike after it was sandblasted wasn't primed first with a rust stop primer than painted, you could have problems. However if there is rust on the INSIDE of that area it could be you have rust eating through from the underside and then appearing on the surface, which is not a good thing and on bikes may not be repairable easily.

I disagree with sweat and road debris sandblasting those areas causing that, why do I disagree inquiring minds want to know? Because I use to live in the Mojave Desert of California for about 14 years where sand covers roads and a person sweats profusely as they ride and my bike never rusted, nor is there any evidence of sandblasting going on, the paint and decals did fade quite a bit from the intense sun but that won't make the bike rust. While the climate of the Mojave Desert is dry I did use the bike for quite awhile in Indiana where I got caught in a lot of rain storms and the bike still never rusted. I use to have a steel bike, a low quality Schwinn Traveler I rode right on the wet sand of the Pacific ocean and would get drenched with ocean water a lot, and other than just hosing it down with fresh water when I got home it too never rusted from the outside, the aluminum components did corrode badly after a long time, and rust did form on the inside after a long time, how long you ask, about 25 years though 10 of those years the bike was stored due to the corrosion on the components that I didn't want to bother to replace. So after 15 years of extreme abusive conditions and lackadaisical care the bike was pretty much done for.

I think too a person needs to keep their bikes waxed with a high quality wax that has no abrasiveness to it (it doesn't say it has oxidation, swirl, or scratch removal capability on the package). Although the bike that I used to ride in the ocean with was never waxed!

Rust.
Kind of like that wee wrong thing you noticed about your first wife/husband, but ignored because of other factors.
Kept coming back, got worse with age, and eventually drove you nuts.

5 years is about right if he:
a) didn't get all the old rust off or treated
b) prepped inadequately

We don't know what you paid him to do, but the kind of permanent paint job you describe is often expensive, because the painter is more thorough in every single area. Which is one reason why a lot of bikes take forever to get painted, and good frame builders either paint their own or keep "their guy" busy and happy, and somewhat secret.

This bike wasn't ridden in the rain - well, maybe 2-3 times - or subjected to heavy sweating. The rust was superficial, not coming from inside. No deep pitting, the integrity of the tube is not compromised. The painter said he doesn't know why, but in his experience rust always comes back. I'm starting to think it's BS...

+1 for Neil Young...

If cleaned and prepped to remove all existing traces of rust, and then if primed with a zinc oxide primer, it should not "come back". If stored in good conditions. Lots of "ifs".


If you got any chips or scratches, (and obviously that's an easy place to get them) and/or the primer coat was imperfect or thin, I would expect to see some rusting. Whether it's the painter's fault or not, really depends on how the rust developed. Imho, rust should not have formed under an intact primer and paint layer, unless as someone mentioned, it came from the inside surface of the tube. The zinc oxide in the primer should have prevented it's development.

Yep.

I would always tend to chemically treat a steel object after blasting, to prevent rust coming back. Blasting can 'seal in' rust in pores on the surface of the metal and this will break out again after a few years.
I used to use 'Metal Ready', which was made by an American company. I'm not sure if it's still available now.? That would create a nice grey phosphate layer on the metal and it helped to stabilise the surface and prevent it rusting through paint.

I've been looking a the idea of soda-blasting frames now. It can be done on most metals and it doesn't disturb the surface very much. That in itself should help keep the dreaded Tin Worm at bay...

Unlike bronze disease iron rusting is not a self sustaining reaction. Iron rusts when you combine it with oxygen and water. Our air contains both so you can see why many things rust, faster in humid climates than in a desert. You can look at older bicycles that have been reasonably cared for versus ones that are left outside and not the speed of rust on the exposed components and through paint.

A good paint job will be resistant to chipping and flaking which tend to be the prime causes allowing oxygen and water at the metal underneath. Those flaws in the paint don't have to be visible to the naked eye to promote rust. After treating the frame little imperfections could cause small flaws in the paint. Five years would be past any warranty I would think. There's a lot of variables involved. Did you clean the bike, inspect it periodically, what is your climate like, did you wax?

Again iron plus moisture plus air = rust.

And yet we find vintage bikes for sale in Florida without rust, here is an example of one that was left in a barn in the Miami area: Barn find. Guerciotti Sprint Campagnolo Triomphe 54cm Less Than 100 mi just one of many examples for sale on CL in the Miami area.

Could be. Maybe sanding would be better?
The bike was always clean and cared for, the very few times it got wet it was dried ASAP, no wax. It was kept in a closed garage when not in use. The climate is temperate and humid but not soaking humid.
But isn't that an aluminum frame? Very similar to an Alan.

Well yeah, if there's no cracks in the paint it will keep the weather off the iron.

My bad, I saw the small pic and posted before I looked at it closely.

Try these: Specialized Crossroads Bicycle - 21 speeds
MEN'S SCHWINN - 10 SPEED - TALL Poorly taken care of Schwinn
Vintage PALETTI RECORD BIKE
Motobecane 60cm Road bike

Anyway you get the picture, vintage bikes are all over down there and they're not rusted out, even the very neglected Schwinn is not rusted out, though it does have some minor rust but that's due to years of neglect as witnessed by other vintage bikes that were taken care of that have no rust. I wanted to show the neglected bike so some of you could understand that steel bikes are not rusting away into piles of rusty powder even if it's neglected...and that bike, and the others I listed are all in a very humid climate in Miami Florida.

Of course they don't, I love steel frames - in fact all of my bikes are steel. In this case I'm concerned about the paint, not the frame integrity, I could sand the rust spots and paint them with some stop-rust and functionally it would be OK.