I don't know that I would say it's a "no no" at all, as long as it's compatable. I know that there has always been a general "rule" drilled inot all of our heads that you have to primer everything, but it doesn't apply with this paint. Look at 69Charger's original posts and he said it over and over, "no need to primer with this paint", and he was right, you can go direct to metal with it, or paint over primer, paint, etc.