Coating on replacement body panels

[Keeper_of_Tess]

Dear All,

I have an 1993/4 LSE and I'm in the process of fitting a new inner wing (front n/s). I've never done this before.

The replacement that I bought isn't exactly right and I'm having to hack it about do some fabrication which consists of cutting pieces off and then folding over the cut edges to give them some strength. The wing came covered in a layer of black primer, it's almost a thin layer of plastic. Where I've been cutting and bending, the coating has cracked and come off. Worryingly, there's some light rust in places where the protective layer has become detached.

I plan to remove the coating where it's cracked off, and where I'll be welding, then treat the metal with phosphoric acid and paint over that with red oxide primer. My original plan had been to simply paint over the rest of the black coating but, in view of the rust that I've seen starting, I'm worried that corrosion will carry on beneath the layers of paint.

 

Two questions then:

1) Is the black coating normally regarded as something temporary, to be stripped off before use; or is it supposed to be the base layer for over-painting?

2) Given the (admittedly light) rust that I've seen, should I strip the whole thing back to bare metal anyway, even if the black layer is supposed to be a paintable base-coat?

 

I hope that the layers that I'm going to apply will keep the oxygen out, but in time some is bound to diffuse in and I fear that the light rust will not be light for very long.

 

Many thanks,

Nick

[Snagger]

It's meant to be permanent, if it's the cathodic primer I have in mind.  Most car panels are done with it these days.  I suspect the panel has been stored badly by the supplier or was coated over a dirty surface that was already suffering flash rusting.  Britpart, by any chance?  It sounds like you're going to have to fully strip and etch the panel, just to be sure.

Nice to see you again.