@hugger I've been working on the latest project. It was "nearly ready for paint" in epoxy primer. Well there was a little rust poking through the primer in multiple spots so I decided to take it down to bare metal. After sanding the fender down I uncovered a giant brown blotch. I can only guess this was a big rusty bare spot at one point and this is the result of sanding it down. Its smooth, almost like a stain at this point. Whats my next step here? I'm guessing it's still rust and will poke its way up through the paint at some point. I was going to hit the sandblaster and try to get it clean, or should I hit it with some chemical treatment or rust converter? Maybe it's ok to spray over? Thanks!
Couple options 1. Ospho will convert whatever might be there,..then epoxy after 48hrs of dry time 2. Light blast from 8in away keeping the wand moving of course then epoxy 3. DA the piss out of it with 80 or 60 grit then epoxy But yea it was surface rust that wasn't completely removed b4 it was primed
Thanks for the reply, Ethan. I'll kiss it with the sand blaster and see what happens. I'll probably treat it with ospho just to be safe.
Blasting can warp it, even if you are careful. Maybe you'll get lucky. Phosphoric acid will remove light rust, may take several applications. Picklex is another good rust treatment, but it's gotten pricey. If I were doing it, I'd use Phosphoric + DA sanding. I would only blast if there was deeper pitting.
If you use fine sand with moderate psi,..35 to 40 on the gauge and keep moving you would be hard pressed to warp anything,... blasting got a bad wrap because of knuckleheads taking their car to industrial places and monument places where they are using 100psi and shooting gravel at the surface,....with ole Donny using his wand with a 3/8 opening in little circles on the surface,....that's why guys are afraid of blasting,..you would have to try to warp something using a home use psi pot
You have to take the surface into consideration as well,.. compound shapes have plenty of strength much more so than the center of a roof or similar
I've never had an issue blasting sheetmetal. I think the psi is in the 75ish range and I shoot at a 45° angle.
Yes, fine media, low pressure, and a glancing angle minimize warping. I've gotten into trouble when I blasted both sides of a panel, even when being careful. You don't notice it until you start to block sand. I don't buy the common belief that heat from blasting warps the metal.... rather it's the peening effect that expands the surface. Now we know about shrinking discs that can repair the damage.
