I am dealing with a similar issue on my 41 PU I'm painting. The PO had the cab sand blasted and then he let he it flash rust before putting primer over it. I removed the primer with a scotch brite on my grinder and it left a light brown tinge even after 180 DA. You can see it here a bit. My paint store called a supply rep and he said to use rust mort on the cab, leave it on till the cab roof turns white and chalky, remove the white with a red scotch brite and epoxy primer over what is left. I haven't had time to apply it, maybe tonight.
Weelll, everyone has an opinion and experience with what works/ worked for them…..I still have my first car, ( 1939 FORD tudor) that had been sandblasted by a commercial blaster with no car experience, big flatish panels warped, lacquer primer applied and left outdoors…she was RUSTY ,!….I , being 15 years along with my Dad sanded the hel out of it with 36 grit 6 inch or so disc grinder discs in hand drills( that’s all we owned) sandblasted the pits with a Sears hand held blaster the size of a paint gun, skimmed the large warped areas with filler …sanded off, more filler sand it off…until I learned how to longboard panels straight as an arrow…..lacquer primer( this was 1975-1977) then lacquer paint….and this was using SILICA SAND that leaked out of railroad cars heading for the glass plant….I was so poor I couldn’t afford the D….I was POO!!….the lacquer is starting to check now but nothing has come off of the metal…
OSPHO sounds like good stuff! I am concerned about water getting between the chrome trim and my rear window. I use a blow dryer but I'm still wondering if ALL the water is gone. When I repaired and painted the "M-word"a few years back, this area was a trouble spot from the factory. I wonder....if I spray some OSPHO along the edge after a wash allowing it to seep in behind the chrome trim ...will that protect the metal from future rusting issue? 6sally6
I think about all this sometimes. Then it occurs to me that I am working on a 93 year old car, and I am 74 years old. The car and I wont be around long enough to see a second restoration. They don't all need to be metal finished. Run a random orbital sander over it, wipe it off with wax and grease remover, spot treat the rust, and weld in patches. Epoxy primer it, and use filler as necessary. Projects that take years, often aren't finished due to changing priorities , and a dwindling enthusiasm.
OSPHO. Use as instructed. Everything that I build has treated rust, patch panels, and filler. Life is too short. I am only 51, and by the time I am retirement age, there might not be gasoline to get to put into anything.
I posted the before pic above, here is last night after I applied the rustmort, let it dry overnight and removed the extra with a red scotchbrite pad on my buffer. It is much cleaner and ready for epoxy primer and body work. Note to self: Don't drill the top of your truck for a spot light. See those white spots on my floor? Use a drop cloth with rustmort!
Picklex 20 works great. Very similar to Ospho. I used it on all the body panels of a '66 Mustang. Some sat for a year or more before painting.