If you just spray primer on ali then yes it more or less just full off, it's basicly like a non stick pan. One way to deal with ali is to prep it throughly with a body shop DA or random orbit sander with a very fine grit pad. You need to make the whole surface uniformaly flat, this is a not a job you want to do by hand. You could use a jitter bug or sheet sander but they are hard work compared to a DA sander. Next step would be to use etch primer flat off then start with colour then clear.
http://cgi.ebay.co.uk/New-Sealey-DAS... tem51953a7859
http://cgi.ebay.co.uk/BERGEN-AIR-TOO...item3a5e8eb0ae