Bicycle Mechanics - Should I paint or powdercoat?

I would like to get my fixed gear beater painted on the cheap. Through friends of mine I can either get the frame sprayed by an auto bodyshop or powdercoated by a fence manufacturer, neither of whom "do bikes". Both will do it "for a case of beer", but obviously wont guarantee the quality. I can also get it sandblasted first either way so that will not be an issue

Which would be the better option? I'm more concerned with durability than looks.

Thanks

Powder coating is a very tough durable finish. Powder is not sold in small quanities so you may have to accept the colors that the fence manufacturer has available.

powder all the way, just make sure they mask off the threaded bits

Before powder, what preparation is necessary?

Powdercoating is the more durable finish. One downside is that with a place like this, that doesn't "do bikes," a badly-done powdercoat finish is very difficult to remove or rework, whereas a regular paint-job can be stripped and repainted, or touched up, much more easily.
Then again, if it's your beater bike, you probably aren't too worried about things looking good. Dangers with powdercoat include too much or too little paint ending up on tiny joints (like cable stops brazed onto the tubes) or paint getting onto bottom bracket threads or inside of headtube where headset cups sit, or inside seatpost. Make sure the areas where you don't want paint are masked well, if you go with powdercoat.

Preparation is similar in either case - the frame should be entirely stripped of its old paint. Can be done with stripper or by sandblasting. You can do the former yourself, and either place might be able to do the latter for you. With powdercoating, it's especially important for the frame to be clean before the paint is applied, because the metal is heated to where the powdercoat actually seats in the "pores" of the metal (or something analogous to that). With a traditional paint job, an old factory-paint job can actually function as an effective base or primer, because it's usually quite well-applied.

I'd go with the powdercoat, too. I agree that powdercoat generally provides a more durable finish, but my reasoning goes a bit beyond that. The experience of your two friends also factors in. The painter is used to spraying the relatively simple surfaces of automobiles. The powder coater is used to spraying more complex surfaces of fencing components. It seems clear to me that the surfaces of a bike frame are more like fencing components than automobiles.

If I didn't know anything else about them, given the choice between two people who "don't do bikes", I'd take the fence guy.

Bikes have several places, like the seat stay and chain stay junctions with the seat tube, that are hard to spray paint. A painter, even a good painter who's not experienced painting bike frames can have voids or runs in those areas. I suspect that the nature of powder coating would eliminate that problem.

Bikes are made of tubeing. Tubes have four sides so a painter who is used to working flat surfaces could have trouble. I'd assume that a fence maker would be experienced in working with round tubes.

Thanks for the replies - it looks like powdercoating is the go. Now I just have to decide between the huge range of 6 colors on offer!

One thing with powdercoating is that the painted item is "oven baked" to liquify and set the coating.

I'd be concerned about an Al that the baking temperature would be enough change the frame's factory heat treatment. A steel frame, either brazed or welded, should be immune to this.

I did a bit of research into the heat-effect issue when I had my frame painted... The consensus was that it's pretty sure that the frame won't be damaged, so I went ahead and had it powdercoated. It's holding up fine so far.
Mind you, it was a cheap frame and I didn't have a whole lot to lose.
Painting by an auto body shop would have cost as much as a powdercoat and a new frame put together...

Will a powder coated finish leave a smooth or grainy surface?

Smooth. Not as shiny as a liquid paint+clearcoat, but not matte either. You can clearcoat over the powdercoat if you want to, but I like mine as it is.

Will a powder coated finish leave a smooth or grainy surface?

If you're comparing to a finish that resembles bikes out of a store, then it would be grainy. It won't be Shiny.

Based on my experience with paint, I say get it powder-coated. You can get powder coating (if I understand it right) with your choice of smooth or grainy, depending on the equipment and skill of the person doing the work.

I'd be concerned about an Al that the baking temperature would be enough change the frame's factory heat treatment. A steel frame, either brazed or welded, should be immune to this.
I've noticed alot of "urban mountain bikes" have powdercoated aluminum frames, to up the cool factor. So damaging an aluminum frame with powdercoat heat shouldn't be an issue if the manufacturers are doing it.

I've noticed alot of "urban mountain bikes" have powdercoated aluminum frames, to up the cool factor. So damaging an aluminum frame with powdercoat heat shouldn't be an issue if the manufacturers are doing it.
Not necessarily. There are different powdercoat products that are baked using different temperature cycles and a slew of different Al alloys that require different heat treating cycles. The manufacturer would certainly know which alloy was compatible with which powdercoat baking temperature and time. I don't think a commercial fence painter would be that sophisticated.