Treating rust with phosphoric acid

[30cabriolet]

In another thread about paint prep, Brent mentioned wiping the body using phosphoric acid. I would like to treat the the inside of the outer edges of my '30 running boards. This channel forms a long tube where rust has formed and I want to stop the rust before I proceed. I also want to hit any areas that I cannot easily get paint into. Does the acid need to be neutralized or can I just pour it in and let it do its job? What do I need to do before I paint over it? I would appreciate any tips.

 

[Pete]

I don't use it for body or paint prep but I do use it to treat camshafts after grinding to hold oil better and etch the "mountains" off.
It definetly does have to be nuetralized after use..For what I do, the
recommended method is HOT (200) water.
For paint prep info, I suggest you talk to Brent on the phone..He is one of the best.

 

[Kevin in NJ]

I would not use phosphoric acid in a tube. There are many variations that you should consider. There are two products, Ospho and PickelX, that do not need to be neutralized. While I am not a big fan of the POR 15 products, inside an enclosed area with some surface rust is one place I would consider. There are also some wax based sealers that are for coating the inside of rocker panels that body shops use. I have used the PickelX product to protect bare metal for extended periods. I did a bunch of sand blasting on metal that needed extensive metal work. I could not put the epoxy right on the parts. After a couple of years the only problem I had was with the rust at the bottom of some pits that were not fully cleaned out. The rust came back in those pits.

http://autobodystore.net/Merchant2/merchant.mvc?Screen=PROD&Product_Code=P20&Category_Code=