I'm writing this for a friend who seems to be ready to chop out every peice of rust in site before he stops and thinks of the consequences. He has bought some acid from Osh, not sure what it is but seems like the same stuff they sell at Home Depot for cleaning rust off of rain gutters. The HD stuff works great! Anyway, should he treat the rusted areas with the acid, grind away as much rust that he can and then weld a few plates on top of the wholes that may be left. Most of the rust that he is battling is in the diver's side floor pan. It's not all that bad, not really a structural issue rather preventative maintenance. I know everybody here seems to love POR15, but other than using that stuff after he has neutralized the rust is there anything else he should do?
One other question, he lives near the beach, so everytime he cleans an area of rust it starts to re-rust again fairly soon. He will not be welding stuff for a few days so I was thinking that he could protect the area by spraying weld-thru primer on it. Has anyone used a type of weld-thru primer before?