I've used this product for many years and can't say enough good stuff about it.... goes on milky white and dries black......underneath where the sun doesn't get at it your done but in an area that gets sun they recommend to paint
over it to stop UV ..... I used to paint
small areas of rusty metal and let it weather for many years and it worked perfectly with no rust again....
I bought the gallon liquid (not the paste) and it took less than 1/4 gallon to do the whole underneath frame and axle
(and it was 14 years old and never done) I did not Scrape or wirebrush anything....but i did give it two coats with about 20 minutes between coates.
This Picture is Untreated:
This Picture is Treated and is now about two months old: