Ok so im fixing a rust spot on my passenger door and plan to bondo once I grind off the rust and get to clean metal. My question is when I go to bondo does the surface have to be completely bare metal, or can some primer be on it. This car is my daily driver so its hard to get done all in one day. I was working on it all day today and now the suns setting and loosing day light so I sprayed 2 coats of grey primer onto it, Can I just sand it lightly then bondo over the paint or do I need to remove it all?

 

Your best bet is to go bare metal and primer on top of the bondo

 

filler will stick much better to clean metal

 

Thats what I thought but I wasnt sure, Ive never used it before.