Sandblasting dark spots left

[MX145]

On my 68 Camaro areas that originally had a little more than surface rust have dark spots after sandblasting. The rest of the car turned out great with the white/grey clean metal color. Do I need to keep sandblasting until the spots go away or use some type of rust conversion process before epoxy primer? I'm trying to avoid using a rust sealer product like POR-15 because I don't want to get the car wet with their metal clean and prep process while I'm working some other bare metal areas. Seems like a lot of pro builders use epoxy right over the media blasted surface and I want to make sure I do this correctly. The spots show up in areas behind the quarters and inner roof structure so they won't need finish paint work. What do you guys think?

[Greg from Aus]

The dark spots are rust deposits still left in the pitting, it needs to be removed, or it will continue to corrode. after it's removed a two pack epoxy primer is the way to go.


Greg

[MX145]

Thanks for the reply Greg.
I tried hitting the same area with a 3M Scotch and 80 grit sanding pads. It looked a little better but wasn't totally gone so I hit it again with the sandblaster. The picture is attached. There's still discolored pitting so I'm not sure where to go from here. I'm not afraid of a little elbow grease so I can keep sanding. I just don't want to take too much metal off.

[Greg from Aus]

You will always have the shadow of the pitting, you just need to get rid of the black oxide. glad I could help.

Greg

[elitecustombody]

I agree with Greg. Get it all out before shooting primer.

[DOOM]

Get it out rust never sleeps!!!

[MX145]

Thanks for the info guys. Seems like I'm using every sanding tool in the shop but I'm getting there! Talked to Barry at SPI today. I couldn't believe how much time he spent making sure I was comfortable with the whole process and understanding the differences in their primer products. Don't find customer service like that very often these days.
I'm hoping to have this thing in epoxy soon. Then it's back to sheet metal and more epoxy. Its been good taking a break from fitting the passenger side quarter. The Golden Legion quarter fit great everywhere except the trunk area. It looks as though it wasn't completely stamped for the deck lid or seal. I've got a few hours into it just to get it to go all the way on the car. Thinking about going with AMD when I order the rest of my metal.

[Denvervet]

I'm no expert but have heard that the media used to blast paint and mild rust won't get the dark black oxides. One has to use a different media....like actual sand/silica which is much harder. You just have to be careful.

[elitecustombody]

MX145, buy a small Speedblaster gun if you have only some small areas, playground sand works just fine for that, just make sure to wear a good respirator

[MX145]

Thanks guys. I got it all out using a combination of wire wheels, sanding discs, and a small sandblaster using sifted playground sand. Epoxy's going on to seal it all up.