This car owner is a "I can" customer and did the bondo work himself.....
After I sprayed on the filler/surfacer I usually spay a very thin layer of over redused (about 150% more thinner than normal) black base.
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Then I blocksand with P320 grit paper. (If you sand with a machine this tip is of no use) and it reveals whether there is unevenness. The dark spots you see are uneven, perhaps 1 or 2 tenths of a millimeter deep. The filler is approximately 4 to 5 tenths of a millimeter thick, so you have 2-tenths to blocksand them away. And don´t sand just the spot, sand the whole panel. At the left on this door you can see the "orange peel" surface of the filler.
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After 15-20 minutes of sanding they are gone. It is a time consuming job, but be patient, it pays.
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An alternative to the black base, is a black powder from 3M, just dust on and sand.
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The P320 sanding is just for blocksanding to reveal and correct unevenness.Not to paint on. Before paint you sand with P400 - P600. And/or you spray on a primer that you can sand with a finer grit.
Do not use Acrylic Laquer, Enamel or Aerosol paint for the "mark paint", as it smear your sanding paper, even when it is dry.
Use a 2 coat base paint, it don´t smear.