"Bruce L. Bergman" wrote in message

If you are going to the trouble of painting, treat the rust first or
it'll pop right back out. As a minimum I would get a needle scaler or
a 4" grinder with a knotted brush, or something to knock the big
surface rust off, then use a rust converter before rusty metal primer.
It will come back again, but not nearly as fast.

I had to replace the seat on my Bobcat recently and used my needle scaler to
remove the rust from the metal base the seat mounts to. I was pleased with
the speed of removal, for heavy flaking rust it can actually work as fast as
blasting with a fairly large sandblaster. You don't have to wear through the
rust as with other methods, it can "peel" or scale layers off. You don't get
a white metal finish but do end up with a pretty tight surface.