surface rust specs under paint, what to do before primer

[Swims350]

Ok so on some old gm bedsides they had rust on body lines and digging into them some specs turned up under the paint. I have sanded them to bare metal with 80, stripped the rusted spots prior that I saw with a rust/paint stripper disc, thus leading to the 80 and attempting to feather the paint back which exposed these issues.

They are just small spots like scratches, lines specs etc. They show up black looking but I'm color blind, so I'd bet they are rusty orange/brown.

I can't blast them, I do plan to epoxy them, and I hear rust reformers/converters are bad to use then prime/paint over?

I noticed I can hand sand them with some 80 and a finger and they appear much lighter or gone? Thing is OMG there are soo many spots, not to mention some large areas. Now by large areas I mean like the top of the bed rail the area a toolbox would sit, that entire surface, like 16 inches or so long by like 3-4 inches wide all has rust left after stripping and 80. I also have pits in that areas. I know most of you know me, I am on a tight budget and in a small town, so trying to fix it cheap, thinking of using the reformer from rustoelum, or maybe vinegar and water, scrub, rinse baking soda, that old trick. I am also thinking maybe jb weld over the pitting area? I know bare min. would need filler. I figured like on my t/a's roof to 1/4 joint, I used some jb weld then body filler. So I was thinking same thing here.


Side note anyone had any luck filling old bolt holes in the tops without welding? Like a backer and then jb weld or something? I know jb weld may not be the best and I could do some kity hair or something if need bem just exploring options. I may break out the welder and do up the holes anyways, I have a cheapo flux core.

 

[bucket]

If it's just the typical tiny little rust specs that are often found EVERYWHERE under original GM paint of the 80's, it's not too big of a deal. I've had great luck with 80 grit on the DA, just like you've done. And on any areas where you can somewhat feel the rust specs, use 80 grit by hand, just like you've done. But for the bazillion little specs that you can see but not feel, I'll treat with an aerosol type rust converter. I don't just leave it there as a base though, because it's not a good one. I will sand it off with 180 grit on the DA, which leaves the little rust specs still "treated". Then coat with a good epoxy primer.

 

[Sad Sack]

Do the best you can with the rust and treat with naval jelly, rinse and primer, NJ is an etcher and works great for sealing them rust streaks. I had a car with mega surface rust on roof, did the best I could to remove it, naval jellied it, primered and used polyester fill, primered some more then painted, lasted three years then sold vehicle and still didn’t return.

 

[Frankenchevy]

You can get phosphoric acid really cheap. It will convert rust and etch bare metal. I’m not a painting expert, but I’ve painted over this stuff quite a bit. $18/gallon at Home Depot.

Klean-Strip 1 Gal. Concrete Etch, Metal Prep and Rust Inhibitor Outdoor Cleaner GKPA30220 - The Home Depot

Remove rust from iron and steel surfaces with this Klean-Strip Phosphoric Prep and Etch. Features galvanized and aluminum finish.

www.homedepot.com

 

[Grit dog]

Oxidation doesn’t occur without oxygen. If it’s rust spots buried under original paint and lasted 50 years, clean it up, hit it with a primer that will stick like your epoxy and move on to the next step.
Pitted spots fill with bindo not JB.

 

[Swims350]

Oxidation doesn’t occur without oxygen. If it’s rust spots buried under original paint and lasted 50 years, clean it up, hit it with a primer that will stick like your epoxy and move on to the next step.
Pitted spots fill with bindo not JB.

I was planning on using filler not jb on the pits, was more thinking the bolt holes with jb.

I would agree with the other as well and was my first thought, how TF did it rust under primer and paint and not show? Well turns out yesterday I found the answer, some or most of it is nothing more then paint/primer, reason it did not come off, low spot like lil tiny dings buried like pencil tip sized. there is some spots that I know are rust because of seeing the rust prior to sanding. I wire wheeled them down as best I could, thus how I found out most were simply paint.

 

[CalSgt]

Oxidation doesn’t occur without oxygen. If it’s rust spots buried under original paint and lasted 50 years, clean it up, hit it with a primer that will stick like your epoxy and move on to the next step.
Pitted spots fill with bindo not JB.

^
This

 

[hoagster]

Vinegar Will neutralize rust also, cleanup easier and is cheaper than harsh chemicals. Use a good cleaner acetone or something similar and a final wipe. Then spray with a good epoxy primer.

 

[legopnuematic]

As far as using a rust neutralizer/acid/etch/chemical, refer to the tds and tech sheets of the primer you intend to use. Some mfg’s like Tamco (what I use) recommend to not use any of those products under the primer.

On the flip side, there are plenty of products that might even recommend such pre treatment or say it’s A-Ok. With how expensive paint and body materials are, I’d be sure to follow the mfg’s recommendations, whatever they might be.