Pinholes seem to be a never ending battle. Here are a few tips to help reduce them. 
  • The first pass of filler should be spread thin, and ‘tight’, which ensures the filler will be pushed into all the scratches and previous body filler. The second pass of filler is where it can be built up. This is not a second batch of filler, just the second pass with the spreader. 
  • Make as many passes as possible with the spreader, this helps work the air pockets out of the body filler. Do not just spread the body filler on with one pass, and you’re done. Keep working it. 
  • Move the spreader slow, and keep the spreader as low or parallel to the panel as possible. 
  • Metal spreaders tend to help. 
  • Fill over 80 grit. Filling over 40 grit has a harder time getting in the deeper scratches, producing more pin holes and nice as nice of a spread.  Also, there’s a chance the 40 grit can shrink more. 
  • Before primer, the pin holes can be filler with the same body filler.  There is a chance with using glaze that it could shrink more than the filler. 
  • Some body fillers are better than others. A recommended filler is 3M Platinum Select.
  • Good polyester primer, such as Spies Hecker, Glasurit, or Standox