Firstly, find out the source of the problem. Why is it chipping? Cheap paint? I haven't had the chance to paint a bumper yet, but I have painted a spoiler, and the process is probably similar, if not the same.
1. Sandpaper. If there are no cracks or bad scratches, #450 will do just fine.
2. Cover scratches and cracks with putty. Leave to dry then sandpaper it until it's smooth.
3. Sandpaper some more. After #450, get some #600, and then #800. I forgot to mention, you'll have to use wet sandpaper, meaning not the usual sandpaper you use for woodwork, but the ones you can use on wet surfaces. The sandpaper process will also require you to use water, and keep the surface wet.
4. After all the sandpapering done. Time to paint. If you're using can spray, then it's pretty much straight forward. Other than that, I'm not sure.
5. Spray one light layer after another until you can't see the old colour/putty/etc anymore. Let one layer dry up before doing the next.
6. After you're done with the spraying process, get some #1000~#1200 sandpaper, and do some more wet sandpapering.
7. Final and most crucial step is the finishing. I use a #3000 liquid finishing. You can use it with a buff, or you can do it by hand, whichever is easiest. Slow circular motion. Do it until you get some good reflection effect, or until you're satisfied.
It takes a lot of patience to do this properly. If you're patience is like a 0.1A fuse, then you're better off sending it to a shop. Good luck.
p/s: I've never used 2K, so I don't know how to use them.
