dealing with surface rust

[MAK]

My new 72 has a good amount of surface rust on the roof, hood and other horizontal surfaces. Same stuff you see on old cars that have sat in the sun long enough for the paint to deteriorate. I've also got a 68 Cougar that has the same problem under the former vinyl top. Problem is I don't know how to deal with it.
I've used an angle grinder with the 3M paint/rust removal abrasive pads on a few spots on the truck and also on the Cougar's roof. It takes the paint and scale right off but I can't get a 100% bright shiny metal surface. About 1/2 of the spots get down to bright shiny metal but the other 1/2 that was more pitted remains discolored (brown or black). Although what I would consider rust appears to be gone and the discolored areas are fairly smooth aside from the pits, I'm pretty sure this surface is not ready for primer, glaze or filler.
I've picked up a few books on paint and body work but nobody addresses this problem. I really need some help from those of you who have worked through this issue. What do I do about the discolored areas? Do I need to use something like POR-15 or some other treatment to kill all the rust if that's what I'm still seeing? Is the rust actually gone and the metal will just always remain discolored because of the former rust or what? Can you buy the stuff that they use to acid dip entire bodies to remove all the rust? I see a lot about using the rust killers/encapsulators but it seems to be more for the frame, floorpans, etc... I don't want to be dealing with rust coming back up from under the paint 5 or 10 years down the road. Any help or direction to helpful info/reading would be greatly appreciated.
Thanks
Mark

[Tim P.]

I would take a small brass wire wheel to the pitted areas. that should take care of the discolored areas. also if you put too much pressure in one area it will discolor the metal a form of burnt look. brass wheel will take care of that. eastwood company claimes that there rust encapsulator product work better than por 15. they did some test that were posted on there web site last week on both products and por 15 didnt make the grade. read up on their site about it then you choose. good luck.

[dcbullet]

Pardon for the bump of this topic but I have the exact same question that MAK did. I was wondering if he came up with a solution or if anyone else had an opinion on the matter, other than the brass wire brush.

Thanks in advance.

[MAK]

Yes, sure did find a solution. The wire wheels just weren't getting me any further than the other abrasives. Worked on both the truck and the really bad project under the former vinyl roof of my old Cougar. Most everyone I talked to and boards I posted on met with recommendations to just coat with POR15 or some other rust convertor and then paint. Finally found a good how-to that explained how to really remove all the rust and not just cover, convert, or stop it. I've got a lot of hours in it but finally got down to 100% bright shiny metal and just have a few patches to weld-in on my old Cougar's roof. You just have to coat with one of the many phosphoric acid solutions, scrub with steel wool and a wire brush for the pitted areas, then wash it off and start over. I've gone through 3 bottles but it works. I can't tell you how many 3M abrasive pads and paper I went through on my DA sander and angle grinder trying to get some bright metal to show through with no success before I tried the naval jelly.

Here's the link where I found out what worked:
http://hotrodders.com/forums/t55679.html

Pardon for the bump of this topic but I have the exact same question that MAK did. I was wondering if he came up with a solution or if anyone else had an opinion on the matter, other than the brass wire brush.

Thanks in advance.

[dcbullet]

Thank you MAK!

[bluef250]

Great solution to a problem most with minimal kept trucks have, my truck. Where did you get the phosphoric acid solutions? Is it available at a well stocked hardware store? You mentioned Naval Jelly is that a phosphoric acid solution?

[tubewatts]

GOD BLESS NAVAL JELLY