Phosphoric acid is a "rust converter" it converts the "red" rust to "black" ferric phosphate, which is then scrubbed off leaving bare metal.
Coke has phosphoric acid in it, lol.
Naval Jelly has a higher concentration of phosphoric acid, it comes in a jelly so it can be applied to vertical surfaces.
It will peel paint.
You can mask off the area and use plastic to cover painted surfaces.
I would sand around the area because there WILL BE rust under the paint around the rust spot, sand back enough so you have good rust free metal around the spot.
Wear rubber gloves, apply naval jelly, work it around with a brush every few minutes, leave it on for 10 minutes then rinse it off with water, scrub surface and check for rust, if there is still some rust then re-apply naval jelly and repeat above.
Make sure to wash off any surfaces that may have been splashed with this acid ASAP.
Paint with Primer after area dries, then a vehicle paint, primer won't stand up to the sun and rain, it is just used to bond to the metal it needs to be covered with an "exterior paint", you can color match later
Last edited by RonD; 05-05-2014 at 09:41 AM.