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#1503942 Tue Jun 06 2023 06:42 PM
Joined: Feb 2020
Posts: 33
Hello everyone,
I was trying to spot sand some rust spots out of my 1950 cab roof and it has now become almost the entire roof. I sanded all the way to 36 grit but as you seen in the pictures this is what I am left with. My question is that black stuff I am seeing is it rust? I cant seem to get it to sand out. You can see the scratches from the sanding but I am not sure if this is just pitting in the original metal and it would be fine to leave or not. Any advice on how to remove or is it ok to leave?
Thank you!

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Last edited by jasrking; Tue Jun 06 2023 06:42 PM.
Joined: Sep 2012
Posts: 201
My suggestion is this...Dupont or some paint supplier may have some type of metal perp which is a mild acid to kill rust...and/or put a thin coat of body filler over it. There are now new primers that are much better than original lacquer primer and you could check with a good auto paint supply and ask for advice. Some etching/activator primer might be a good choice.

Joined: May 2015
Posts: 8,073
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
Yeah, you've got rust pits in the roof. Not uncommon. You can try using a wire wheel if the pits aren't too deep. Phosphoric acid (aka Ospho) available at your local hardware store will convert the rust to iron phosphate, but most epoxy primers (which is what you should use) aren't compatible with phosphate treated metal. Check with your primer supplier. Evaporust makes a gel product which is different than Ospho, and will remove the rust, however, I'm not sure of the compatibility with epoxy primers. Again, check with the paint supplier. The REAL way to get rid of rust in pits is to sandblast, then immediately prime after a grease and wax remover wipe-down.

Newest Project - 51 Chevy 3100 work truck. Photos []
#2 - '29 Ford pickup restored from the ground up.
First car '29 Ford Special Coupe
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Joined: Feb 2020
Posts: 33

Joined: Oct 2005
Posts: 4,038
"Hey! I sound like Darth Vader!!
I'll typically sand with a 40 or 60 grit and work my way up to a 180 grit. If, while sanding, I still see orange dust being made, I keep sanding. If I don't, I chalk the dark area to stain and move on. I haven't had any paint work bubble to date. And some of my epoxy primer jobs are going on 11 years!

Joined: Mar 2010
Posts: 10,724
Renaissance Man
I would go to town with a red Scotchbright pad by hand on those areas. It gets into recesses better than sand paper and you won't risk making the metal too thin. If you do use Ospho, make certain then you diligently scrub off the area to remove any excess dried on Ospho and the white powdery residue left behind. This powder is a byproduct of the chemical process. I use a red Scotchbright pad moistened with Ospho to do this cleanup. Again, the Scotchbright pad gets into the depression nicely.
This additional application of Ospho used for cleanup will not create more powder since there is to iron oxide present to make a reaction.
Clean up with your favorite degreaser before applying epoxy primer. I use acetone. Wipe it on with a wet lintless cloth and immediately wipe it with a dry lintless cloth. Do this until the dry cloth remains clean.

Joined: Feb 2020
Posts: 33
thx again..will try the scotchbright followed by the ospho

Joined: Mar 2010
Posts: 10,724
Renaissance Man
If you do end up sealing the bare metal with epoxy primer, just make sure to do a thorough clean up of the metal first.
Failure to do that will ruin any kind of primer.

Joined: Jul 2003
Posts: 132
I'm also an Ospho user. I scrub with red pad and after it drys hit it with 120 on the sander before epoxy. But I use an Epoxy that is intended to be used over acid based treatments. Some, such as Southern Poly do not allow that. Read the spec sheets to be sure of yours. I chose Kirker 'cause it works for me and is reasonably priced.

KENC #1504652 Sat Jun 10 2023 09:37 PM
Joined: Aug 2018
Posts: 669
I was not aware that some Epoxy primers were acceptable for use over Ospho. I have some Kirker Epoxy here. Are you saying that it OK to use it on top of ospho. If so, that would simplify another little project that I'm working on.

Mike Burns
1940 Chev 1/2 ton
1953 Chev 1/2 ton
1953 Ford Victoria
1950 Studebaker Starlight Coupe
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