I have a fender apron that I bought a week ago. Not painted when bought and is already starting to develop just a hint of surface rust.

Should I go ahead and clean the metal off then prime it now or will this interfere with spot welding it in a couple of weeks from now?

 

you want bare metal where you weld or weld-through primer if you're welding somewhere you can't get back to later to prime. cleanliness is extremely important to weld quality.

it won't hurt to prime it now but wherever you weld will need to be cleaned before welding and then re-primed.

 

I guess the answer depends on access to the panel. how easy will it be to finish the panel once it's welded in? both sides? what good is a rusted panel? I'd say clean it up, and buy some weld through zinc primer to protect it until you actually weld it on.

 

That little bit of surface rust will just wipe right off with metal prep. Metal prep is a dilute solution of phosphoric acid and the rust will just be gone. When you get ready to weld it, just wipe it with metal prep and then wipe again with acetone and you will be fine. Shoot a little weld through primer on the part that laps and you won't be able to get to.

 

if its gonna sit for a while Id get something on it, wd-40, paint, or something else.

i second the weld thru for hidden areas.

 

If it is just surface rust and it is sitting inside then it won't matter. The metal prep will take the surface rust right off. I'm quite sure it will take all of that little surface rust off, but if any does remain it will neutralize it.