Hey everyone,

So here is the poop. Cab completely sandblasted, all dents removed, all major rust repaired or replaced (cab corners, rocker panels, driver side cowl, floor, transmission cover, etc...), and ready to lay down some corrosion resistant primer. I chose PPG's NCP 271, recommended by the local auto body supplier, whom I trust.

To clean and condition the metal, I used PPG's DX579 Metal Cleaner/Conditioner. A water based solution you spray on, and then rinse off with a sheeting action. Okay.......now the whole cab looks like it just flash rusted right in front of my eyes.

I looked everywhere on line to see if this what was actually happening. I read in more than one place that the phosphoric acid in the cleaner reacts with metal, leaving a golden brownish coating, which will help the paint adhere.

Has anyone used these products? What has been your process in priming sandblasted metal? I think this is a really important step, since every subsequent coat of primer/topcoat/clear will lay over this initial primer. If this primer were to fail, I would imagine everything on top of it would just flake or peel off as well.

Thanks in advance for any input.

 

Jeff, you might want to post in the bodywork forum and see if you get an expert over there to help out.

 

I'm probably not going to be a big help here, and the answer to your questions mostly lie within a phone call to tech help or an engineer at PPG, but here's a little background you might find useful...

Atmospheric moisture, water itself, or water with anything in it that reduces the pH of the solution below ~10 will cause carbon steel to corrode. Chlorides (from atmospheric pollution or the ocean if you're nearby) and other halide ions in the air or water will accelerate the rate of corrosion by increasing the conductivity in the water. Increasing temperature has the same effect. Within reason, the lower the pH, the higher the conductivity, and the higher the temperature, the faster the rusting. Even dilute phosphoric acid in water will have a pH of 2 or 3, so the formation of surface rust very quickly is not that surprising. Phosphoric acid is used as a metal prep solution since phosphates act as corrosion inhibitors and work to slow the corrosion caused by the lower pH of the acid solution, but phosphoric acid will cause rust to form on carbon steel, just slower than most other acids. So, the fact that you have a layer of rust on the cab is not surprising. I'm guessing it's by design, and that PPG makes a rust converter product that should go on next, or their primer is designed to act as a rust converter to form a good adherent base coat for the top coat to stick to...but I'd check it all out with PPG.

Buzzed over to the PPG auto-refinishing home page (http://www.ppg.com/cr-refinish/phase1/frmHome.asp) and briefly looked into the DX579 product. Looks like you're supposed to use DX520 on it next...but I'd still call tech folks...

Sorry...got a little chatty...slow day here

 

I just had the cab of my project 56 BW sand blasted and then we sprayed with PPG DP90 epoxy primer sealer. This should take care of any future rust.

 

Phosphoric acid turns rust black, making an iron phosphide. If you are seeing brown it would sound like rust to me...Fox

 

I agree, check with a autobody place and see what they suggest for metal treatment.
I've used the phosporic acid wash and it seemed to work well. As for the primer I've used what they call Poly Primer sometimes called Liquid Bondo, it's very thick so get a cheap throw away gun to shoot it. It filled pits, scratches and probably eliminated much spot putty. I've had great success with this stuff I think Dupont, Sherman-Williams and others make this. Good Luck, Dylan1952

 

I use SEM Rust Mort (phosphoric acid) to treat body panels. It says to wash with soap and water after treating as it does not react with non-rusty metal. I always dry sand the flash rust with 220 just prior to priming with epoxy primer.
jt

 

I went through the same basic process on my sandblasted frame, fenders, hood, and my also did my new box. It turned the same light brown color after it air-dried. I used the marine-clean products, probably the same basic chemicals. It works really well and puts a nice zinc coating on everything.


Gary