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powdercoat though which is a treatment I feel has no place on a bicycle but that's another conversation
I am interested to hear your thoughts on this!
Cupcakes-
I think it’s too good at hiding what’s going on under it.
There’s no anti corrosive properties of powder coat like there might be with primer/paint.
Additionally (and this is an issue with people doing the work not the process or material itself) I think frames are often blasted too aggressively by powdercoaters resulting in thin spots and warping/stresses. I was told by someone that works with sheet metal that they can’t blast just one side of a workpiece, doing so causes it to warp, you have to then blast the back to get it back to (near) flat again. I don’t think that can be good for a frame and I think I’ve seen the result of that in having to repair cracks in frames that have been powder coated.
It’s also a cunt to work with, if doing repairs etc.
M_V
Yeah, we aren't talking a tube filling up with water from being ridden through a river etc, small amounts of water vapour, moisture from the air, etc get in (temperature and pressure changes can effectively 'suck' moist air into a tube through a very small aperture) and this can, in my experience*, accumulate enough to be sloshing around inside a 'sealed' tube.
*Yes, I've cut up more than one frame that had no breathers and had ancient, stinking, rusty liquid pour out of the tubes.
I'm not saying every frame without breathers is destined to rust but my experience is that non breathered frames are generally in a worse state than those with breathers.
And I do find it quite ironic @TvH that you are pointing us to videos of someone who doesn't put breathers in his frames talking about having to fix rusty tubes. The video where there's a hole in the back of a seattube, in my opinion probably wouldn't have happened if the seattube was vented into the bb shell. He is also talking about powdercoat though which is a treatment I feel has no place on a bicycle but that's another conversation.
In the case of Vaz, if he is brazing and not soaking I find that concerning as while you can blast the outside of the tube fine, the only way (I know of) to get flux out of the inside of a tube is to soak it out. Maybe he's using a gas fluxer and that might mean that there is no flux inside the tube, I'm not too sure how that works.