Adam
Well-Known Member
Surface rust can successfully be removed or rendered inert from bare metal with metal cleaner or metal etch products containing phosphoric acid, such as “Ospho.” You can find it at Walmart, Home Depot, etc. It is a bit expensive but you generally dilute it 3 parts water to 1 part acid.
You can mix up a batch and soak parts (nut/bolts) in it for awhile, don’t leave them in for more than a day or you will get some pitting/rough surface. This batch can be used many times over, even though it gets dirty.
For body panels I generally mix up a 3 to 1 batch in a spray bottle. Spray an area no bigger than you can manage, like a fender, hood, etc. because you do not want this stuff to dry on the panel. Spray the panel and scrub it with a Scotchbrite pad. Wipe off the area with paper towels to kind of clean up the mess.
Next, wipe the panel with a much weaker solution, like 10 parts water 1 part acid.
This is because the 3-1 solution will leave a sticky residue on the metal that will dry to a chalky but tough film. Most of these products instruct you to rinse the metal with water after treatment, but I found this usually causes flash rust; this is why I wipe it down with the 10-1 solution, which leaves a clean rust free area. Black spots are converted rust and will be ok to paint over.
Then I will generally wipe the area with wax/grease remover before spraying with epoxy primer. Epoxy primer will seal the metal pretty well and the parts can be stored indoors for a long time with no ill effects.
Phosphoric acid is not super corrosive, it is in Coca-Cola in tiny amounts. But this stuff is much stronger and will discolor painted areas, cement floors, etc. So use gloves, but if it gets on your hands just wash em and you will be ok.
Etching primer has phosphoric acid in it and generally serves the same purpose; some paint problems have been reported when painting epoxy primer over etch primer, but I have done this many times, over many years without issue.
You can mix up a batch and soak parts (nut/bolts) in it for awhile, don’t leave them in for more than a day or you will get some pitting/rough surface. This batch can be used many times over, even though it gets dirty.
For body panels I generally mix up a 3 to 1 batch in a spray bottle. Spray an area no bigger than you can manage, like a fender, hood, etc. because you do not want this stuff to dry on the panel. Spray the panel and scrub it with a Scotchbrite pad. Wipe off the area with paper towels to kind of clean up the mess.
Next, wipe the panel with a much weaker solution, like 10 parts water 1 part acid.
This is because the 3-1 solution will leave a sticky residue on the metal that will dry to a chalky but tough film. Most of these products instruct you to rinse the metal with water after treatment, but I found this usually causes flash rust; this is why I wipe it down with the 10-1 solution, which leaves a clean rust free area. Black spots are converted rust and will be ok to paint over.
Then I will generally wipe the area with wax/grease remover before spraying with epoxy primer. Epoxy primer will seal the metal pretty well and the parts can be stored indoors for a long time with no ill effects.
Phosphoric acid is not super corrosive, it is in Coca-Cola in tiny amounts. But this stuff is much stronger and will discolor painted areas, cement floors, etc. So use gloves, but if it gets on your hands just wash em and you will be ok.
Etching primer has phosphoric acid in it and generally serves the same purpose; some paint problems have been reported when painting epoxy primer over etch primer, but I have done this many times, over many years without issue.
