I've naval jelly a little in doing body work...when I was out of everything else. But I agree, that stuff that comes in a spray can and doubles as a primer seem to do better in bodywork applications. In either case, ALL loose rust must be removed. Wire brush on power tools works well for that. If the rusted area doesn't turn black, you didn't remove enough of the loose stuff. And it won't work...or at least as well.

What Naval Jelly is really good for in my opinion is where there may have been light rust which in turn stained non-rusty surrounding surfaces. DOn't know htat I would try it on paint, but it is great for chrome. I was at a fellas place when I was younger, and he had these rusty chrome wheels. They were pretty much brown. He pointed out that the rust was only in a few spots in a crack, and he went to work with the naval jelly. Damned if those wheels didn't look near new when he was done.

For that sort of application, naval jelly is a must have in any garage in my opinion...

-Matt