How to best remove surface rust before Epoxy primer

[merbesfield]

I have a 57 356A Porsche that the previous owner stripped the paint off of 2 years ago and then did nothing. It has been indoors but is still covered with a nice layer of surface rust, some fairly thick. Nothing cancerous, but using a DA with 80 grit is not doing much to it. I tried using Navel Jelly, Phosphoric Acid, and it worked, but took a long time and still seemed to leave a lot of rust deep in the scratches left behind from when the PO removed the paint. Looks like he used a pretty aggressive grit level when he removed the paint. I have sand blasted exteriors with great results before without warping the panels but was hoping to avoid the mess associated with this process. Any ideas? I want to get the car in Epoxy Primer but do not want to cover rust left behind. Do I need to let the Jelly work longer? If I buy the gallon of Phosphoric Acid is it more concentrated than the Navel Jelly brand? I left it on for 15+ minutes and had to do a lot of work with a brass brush to even get these results. I can't see doing this to the entire car. Thanks for the help.

[Len]

If that car was in our shop we would spray about a square foot of Picklex 20 on the surface work it in with a scuff pad then wipe it off and move to the next square foot. After the entire car was treated we would do our body work because the Picklex would protect the metal from further rust and after the body work we would scuff and epoxy prime the entire car then apply our 2K primer, guide coat, block sand and paint.

[merbesfield]

If that car was in our shop we would spray about a square foot of Picklex 20 on the surface work it in with a scuff pad then wipe it off and move to the next square foot. After the entire car was treated we would do our body work because the Picklex would protect the metal from further rust and after the body work we would scuff and epoxy prime the entire car then apply our 2K primer, guide coat, block sand and paint.

Len, does the Picklex 20 get the rust out of the sanding grooves and pits? After body work and before applying the EP, would you DA the entire car, if so what grit would you use? Thanks

[Len]

Len, does the Picklex 20 get the rust out of the sanding grooves and pits? After body work and before applying the EP, would you DA the entire car, if so what grit would you use? Thanks

You must remove any lose rust then the Picklex will convert/stabilize any remaining rust and, in most cases, it will make minor rust disappear. Before applying epoxy primer we would either go over the surface with some 180 or 220 on a DA or by hand.

[merbesfield]

I have done some research on the Phosphoric option and there seems to be some people who are addiment that it should not be done prior to epoxy paint. Barry with SPI is among one of those that says to never use it. I understand there are always those that do and don't do certain paint steps, but I was hoping to use his epoxy paint system. What do you think is the reason that some people have had epoxy issues with Phosphoric acid rust treatments? I just want to be sure to get it right. Thanks

[autobodytech43]

not neutralizing it thoroughly can give you adhesion issues. It's just one of those things...Some people believe in using epoxy directly after sanding and leaving clean metal, and some like to use a metal conditioner. It's just a matter of opinion.
I think if there's pits and it's not blasted or you haven't used a geared wire wheel w/ the handles to get into the pits than a conditioner is an option I'd go with. If you had it blasted or used the gear wire wheel than there's a noticeable difference in the look of the metal and you'll know it's clean, and in those cases no conditioner is needed, in my opinion. In your case, sounds like conditioner won't hurt. There's a HUUUUGE differeence in the look of the metal when it's sanded compared to how it looks when it's blasted and wire wheeled(with the right tool). Again, this is all a matter of opinion, and keep in mind, Barry sells paints and primers so he's gonna naturally say conditioners are bad. If it rusts it's not his issue, but you may call him with adhesion issues. Then again, I hear he's a real straight shooter.

[metalmadness]

If that car was in our shop we would spray about a square foot of Picklex 20 on the surface work it in with a scuff pad then wipe it off and move to the next square foot. After the entire car was treated we would do our body work because the Picklex would protect the metal from further rust and after the body work we would scuff and epoxy prime the entire car then apply our 2K primer, guide coat, block sand and paint.

You can also vinegar water the rusted surface.