When you watch TV programmes like Fantom works new metal is welded in ,ground down then covered with a skim of filler before painting . If the bare metal is exposed for a few hours it gets microscopic rust on it ,the polyester filler is porus even if the paint is not so how do we go for corrosion in future?

 

Interesting isn't it. I always used to spray with red oxide immediately, sometimes paint with rust killer first too. What the modern technique is I dont know, but I may be finding out with rear N/S wheel arch at the bottom.

 

All the panels are galvanised today ,well zintex but if you have cut some out and welded in a patch then that protection has gone.
Maybe ask for us when you take it to the shop.

 

40 years ago we would either spritz bare metal with phosphoric acid or prime with marine grade epoxy primer, depending on when we would begin beating, filling, filing and dry finishing with 80 grit.