I recently ordered a small 2" circular pneumatic sander to aid with repairing some depressions I created in a couple spots on the bottom wing skins when rivetting, and tonight I gave it a test run.
I'd previously filled a couple low spots with some resin/flock mix (flox) and this small sander is ideal for sanding the area smooth without also sanding away too much of the surrounding skin material.
I sanded with various grit papers, going through 120, 240, 600, 1000, and finally 1800 grit to give a very smooth finish. I then wiped one of the areas clean with some isopropyl alcohol and sprayed with primer. Once dry you can check how effective your sanding efforts are ..... no obvious depression ..... all good.
Sanding back the flox filler
Another spot that's now smooth again
Sprayed over with some primer to check for depressions
