Originally Posted by
FastJake
No, yes.
You can simply sand a little to get a rough uniform surface. I would not recommend sanding down to bare metal. It will be way more work, and then you have to prime really well to get it to stick.
As long as the bike isn't rusty just sand it lightly. Then get it REALLY clean, with alcohol and towels. Then prime and paint! Make sure to use several thin coats like the can says or you'll get unsightly runs.
I like working on crummy old bikes so I've rattle can painted a lot of frames. My personal experience is pretty much the exact opposite. Whenever I've tried to cheap out by not removing all of the old paint, the result has been that the new paint chips off easily. When I've taken the time to strip the frame down to bare metal, the paint has been much more durable.
I haven't experienced difficulties with primers either. My fixed gear conversion is a Raleigh Technium frame with aluminum main tubes and a steel main triangle. It was stripped using a chemical stripper and primed and painted using Rustolium products from the hardware store. I painted it around 3 years ago and it still doesn't have a chip anywhere.