Cosmaline? COATING???

[uricad]

What is the gray metal coating that comes on some sheet metal and tubing? It's not sticky--I think cosmaline is sticky... I need to now if I can PC over it if it's cleaned well. I usually blast it off, but I have a large batch of parts with
this coating on them and I'd rather not strip it all off.

[BottleFed70]

Are you talking about a zinc coating AKA Galvanized?

If so, I believe it will need to be stripped.

[CarWiz]

I'd agree. Sounds like zinc and if it's grey, it's oxidized and at least needs to be treated to bring the shine back. PC'ing over oxidized metal will give you nothing but heartaches. Just about any mild acid will strip the ZnO but it's faster with one of the stronger acids.

[Harleydad]

If it's hot rolled, you could be talking about mill scale. It's best to remove it. You can coat over it but if the scale releases from the metal, so does all your work.
Got any pics, it may help to indentify whats on it.

[uricad]

It doesn't look like galvanized. The parts are brand new-control linkage for an airplane (rudder/yolk....) It looks like black iron sheet metal, has the same type of gray non-sticky coating. I will post some pics Tuesday.

[uricad]

Originally Posted by CarWiz

I'd agree. Sounds like zinc and if it's grey, it's oxidized and at least needs to be treated to bring the shine back. PC'ing over oxidized metal will give you nothing but heartaches. Just about any mild acid will strip the ZnO but it's faster with one of the stronger acids.

It was never shiny, it's some sort of protectant coating I think.