I have a customer with a nova that has had the roof repaired since it was restored. Well the roof began to bubble in a few places so I immediately thought of rust. I am normally a collision guy and do not like to work on projects like this but this is a faithful customer. Once I took the paint down it was indeed rust. Apparently the previous shop that repaired the roof took it down to metal and did not prep correctly and the entire roof skin has a little bit of surface rust underneath all the layers. With all that said it is cleaning up nice with a grinder, but there are a few spots that still has a little rust even after I have hit with a grinder. I have attached a picture so you can see what is left. My question is how should I prep these spots with rust left before I spray epoxy?