prepping for painting

[DMedal]

I'm starting to do the cosmetic stuff on my tractors and thought I'd redo the fenders on the hauler I'm rebuilding as practice. The trailer sits out back but I'd have to look at the tractor hood for long hours. Anyway, wirebrushing 30-40 year old paint on the fenders with rust spots and it comes off real nice. I'm left with nice shiny steel with darker (charcoal grey, not brown) spots where the rust was. More brushing doesn't help. There's nothing you can feel with your finger, it just looks a little different. Should I sand or will the primer stick to it? I don't want to sand if I can help it as the metal is already nice and smooth. thanks. -Don

[DeltaBravo]

I would sand it as there is probably rust underneath. Verify by sanding the area a bit. For the whole tractor, a rubber block, palm sander or DA sander will do the job depending on how many spots there are and the time you want to spend. 60 or 80 grit to scratch the rust down to metal, then 150, and finish with 220. Lightly sand between coats of primer with 240 or 320.

[xenon172]

In addition to sanding as DeltaBravo suggests there are several brands of rust treatment / inhibitor products available at hardware and auto parts stores that do a good job treating residual rust and provide extra protection for the metal.

[Tom_Byrne]

AutoZone (in my area, at least) sells a rust converter that you brush on lightly- it converts the rust to a black primer. Then prime the bare metal piece with self etching primer and you should be OK.

[HubbardRA]

The rust converter Tom is talking about causes a chemical change in the rust (iron oxide) to iron phosphate (the black coating). Phosphate coatings are commonly used to prevent rust.

[DMedal]

thanks guys. I gave it a light sanding and painted it. I'll do a better job on the tractors, this is "just" a hauler, a boat trailer that I'm putting a deck on and will get more use of as a tractor hauler. -Don