Originally Posted by toastie
A friend of mine has a new Airstream that has a small blemish, what is it and can it grow. (see attached pic.)
Research "filiform corrosion". It's almost unavoidable. Airplanes suffer from it too.
It's usually the result of oxygen getting thru the clearcoating at the edge of the panel and progressing from there. It must be stopped or will continue to spread.
Remove the clearcoating (Scotchbrite or abrasive paper. Always use a straight motion, not rotary to avoid polishing issues. I recommend lengthwise motions, along with the "grain" of the metal. Do not use a rotary/mechanical device or you will "burn thru" the clearcoating which will result in a browned/burnt residue which is hard to remove.) Remove the corrosion with a "scotchbrite" pad, polish it "with" the grain of the metal (likely length-wise), clean with alcohol, then recoat it with automotive clearcoating available from auto paint suppliers in fingernail-polish-type touch-up bottles and aerosol cans.
Also a pen type: https://www.amazon.com/Dupli-Color-S...+up+clear+coat