Wing step on skin prepare and prime

I want the rivets heads to have primer underneath them. Previously I would use a soldering iron to cut strips out of the plastic coating. I found however that the scrubbing with acid would sometimes lead to small quantities of acid to be trapped despite rinsing. On drying and subsequent removal of the plastic there would be small salt deposits on the metal, with very slight erosion of the metal surface detectable. This was observed with the flap skins, but fortunately these blemishes could be easily sanded out, indicating they were purely surface effects. Nonetheless I have abandoned the practice of slotting the plastic coating, instead removing it completely and spraying lines of primer on the exterior surface. Any excess can be easily removed, particularly if I switch to an alternate paint system.

All holes, edges deburred and smoothed. Some 3.3mm holes were irregular, so were cleaned out with a #30 chucking reamer. Also many burrs were removed with 400-600 grit sandpaper before final brief use of a deburring tool.