Phosphoric acid and steel wool

Freaking works

There was about 3-4 years worth of oxidation prior to starting.

An example of the before from another body panel

What are you trying to do here? I need more context.

Yeh, I'm wondering what you're trying to do as well

Remove the surface rust from a 90s Mazda that had to notorious flaking white paint issue. Stripping it down to bare metal to primer than paint. 

when I called it a night tonight. I'll be back tomorrow to go over the quarters and doors again. But she's about ready to be cleaned off for masking and primer. 

Are you wire brushing and then phos acid?  Or using them together at the same time?

If you are wire brushing and then applying phosphoric acid, why do you think that is better than a rust converting primer?  Or what documents did you use to determine that?  I'd really like to read that, since I'm doing repair on my Miata, and would like to apply some of the same to places that I have a tough time reaching.

Please, more details- this is very interesting.

Add me to the "if this is a quick easy way to get bare metal walk me through it" list!

Phosphoric acid and 120 grit aluminum oxide sandpaper seems to be the hot ticket. The paper will gum up quickly so have about 8-10 sheets per a body panel. I'm spraying the phosphoric acid down using a spray bottle then using a palm sander with the sandpaper. Think as if the acid were quick detailer and the palm sander a clay bar. The black converted material will turn to a thick gummy grey material under the friction and pressure from the sander. Hot water and a quick dry is going to be tested today for a quick and dirty prep for primer. One thing to note, a nylon bristle wheel hooked to a drill worked even better than the sand paper and didn't create the grey sludge. But coverage wise it's not faster and with a cordless drill you'll be swapping out battery packs frequently. But using one of those nylon bristle wheels on an air setup or even a corded drill would work well, especially in tight fitting areas and detail work. 

A follow up question- why do you wire brush the surface instead of wash off with water?  Is that a key part to the change in procedure?

In reply to alfadriver :

I used the brush (nylon seems to work much better than metal wire) and sandpaper while the surface is wet to encourage penetration and ensure complete coverage and saturation. Once the phosphoric acid has dried (leaving a protective but fairly thick and gummy protective coating) I'll be using water and degreaser to remove the coating before tack cloth primer. 

After getting down to bare metal and the surface finish you want a wipe down with the phosphoric acid and leave the black finish it produces. The black finish promotes adhesion of the primer plus also protects metal from flash rust if there is a lag time between cleaning and priming.