I am in the process of sanding down my car to paint it and there is a huge crack in the front lip and bumper. Can i fix this? Should i just buy new parts?

Also I am dry sanding it with 220 grit and then i will wet sand it with 320 grit. Im new to this really, i know i dont want to bullseye on any edges which is why im blocking it instead of using a dual action sander. But how do i know if i have sanded it enough for the primer to stick (I am changing colors from red to black) i get a nice white film when i sand and when i whipe it off the paint looks more dull. In some spots it is very hard to avoid bullseye, am i doing it wrong? Any advice is helpful thanks.

 

I've been using a cheap spray paint primer and it says to sand with 320 before you put it on, I would imagine if you go over a couple times it should be good...

 

You can repair the urethane pretty easily. Just carve a V shape into the entire crack, scuff it with coarse paper, clean it very well with laquer thinner, then apply a urethane body filler.

If you are getting fish eye, that means that the surface has contaminants on it. You need to clean it very well with laquer thinner or something comparible before painting.

 

You can see in this pic where I filled the camaro emblem, took care of a couple cracks, filled some massive scuffing on the front of the GFX, filled a larger low spot on the GFX, filled 2 holes that were drilled for a liscense plate, and filled 2 small abrasions on the very front of the nose. It's been holding up great, and once you get it sanded you can't feel the difference in surfaces with your hand.

 

I have outlined a repair procedure here
scroll down towards the bottom for the procedure, (It's for a small hole but the procedure is the same for a split.)