Heavy file marks showing through topcoats.
Deep scars left by coarse files without sufficient filling from undercoat and putty applications.
a) Sand file marks with an orbital sander, or wet or dry paper to eliminate deep gouges.
Fill with adequate applications of undercoat and stopper. If file marks are already showing, sand to smooth surface and refinish with undercoat, apply stopper, undercoat gain, then spray topcoats.