Surface Rust

jcpettit

Promoted Users
I have a customer with a nova that has had the roof repaired since it was restored. Well the roof began to bubble in a few places so I immediately thought of rust. I am normally a collision guy and do not like to work on projects like this but this is a faithful customer. Once I took the paint down it was indeed rust. Apparently the previous shop that repaired the roof took it down to metal and did not prep correctly and the entire roof skin has a little bit of surface rust underneath all the layers. With all that said it is cleaning up nice with a grinder, but there are a few spots that still has a little rust even after I have hit with a grinder. I have attached a picture so you can see what is left. My question is how should I prep these spots with rust left before I spray epoxy?
 

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Your best bet is probably a stiff wire wheel spot blaster, just watch your temperature with the wire wheel.. This rust in pits is the biggest problem, its probably all rusted on the inside. Nobody here really seems to go for the converters on the market that are supposed to help this problem, the only one recommended is Ospho, but you have to make sure all the white powder is rinsed away before epoxy..
 
I'll second using a power rotary wire wheel & hit it from several directions can help also. Rusted roof likely was sanded only, leaving rust in pits.
 
The wire wheel will only polish the rust in place, the spot blaster will prob get the rust but will prob work harden and stretch the metal leaving high spots that have to be shrunk back down, but much better imho than a wire wheel. Phosphoric acid based rust remover is what I would use, saturate paper towels on the rust spots and lay some saran wrap over it to keep from evaporating. No longer than a two of three hours at the time without refreshing, until the rust is gone. Clean per Barry before priming. Twin or triple etch from DuPont, or Rust Blast from KBS etc... Do not under any circumstances use muriatic acid!
 
Spoke with car owner yesterday and he has actually had the roof repaired since the car has been restored. He mentioned that he remembers the previous shop taking it to the metal and sat a week or two while he was doing filler work before it was ever primed. As humid as it stays here in Mississippi I am guessing the previous shop did more harm than good when they repaired.

Also per Barry's recommendations I will try using Ospho for this one. I will most likely give Barry a call when I start to ensure that I use the correct procedures to rinse and clean before epoxy is sprayed.
 
This should be a lesson to those who think they need to strip their entire vehicle and prime it all at once. For most hobbyists and even many shops, it's best to only strip what can be primed immediately, as in same day. It's the safest way to avoid rust and contamination that will cause problems later.
 
Spoke with car owner yesterday and he has actually had the roof repaired since the car has been restored. He mentioned that he remembers the previous shop taking it to the metal and sat a week or two while he was doing filler work before it was ever primed. As humid as it stays here in Mississippi I am guessing the previous shop did more harm than good when they repaired.

Also per Barry's recommendations I will try using Ospho for this one. I will most likely give Barry a call when I start to ensure that I use the correct procedures to rinse and clean before epoxy is sprayed.

That is bad news anyway, I could see if he was waiting while they were doing metal work, patches, welding, but it also means there is no epoxy under the filler if they were doing that work on bare metal.
 
That is bad news anyway, I could see if he was waiting while they were doing metal work, patches, welding, but it also means there is no epoxy under the filler if they were doing that work on bare metal.
That is correct. I started stripping it down and the top layer was a single stage paint, then a layer of primer, and then filler in certain spots with nothing under the filler. The rust under the filler was much worse than the rest of top.
 
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