When to Stop Sanding

When block sanding polyester primer, how do you know when to stop sanding?  The point of polyester primer is to help straighten the body work, fill minor imperfections, and have a harder and more uniform surface. While polyester does help straighten body work, it should not at all be used as a crutch; do your absolute best work possible in the body work process, and prime over 150 grit.

Polyester is a very good product. It’s also a primer that’s harder to get genuinely flat. This requires starting to block sand with 100 grit and True Blox. 

Here are a few tips:

  • The minimum amount to sand polyester with 100 grit is until there’s absolutely no texture or orange peel in it.  If it’s not actually flat, it will be very difficult to get your paint flat enough. 
  • In theory, and almost always in practice, you should continue block sanding until the primer is uniformly sanded. 
  • Do not cheat. If (and when) there’s an area that isn’t being sanded, it’s still low!  The goal is to straighten it, not just sand it. So don’t dig out the area even more just to sand that area. 
  • The goal is to not have the polyester sanded through. 
  • If it does get sanded through, you’ll have to make some judgement calls.
  • Sometimes there might be some more body work required to correct the low areas. 
  • Sometimes there will be enough primer to straighten the area. 
  • Sometimes you might need to re prime, depending on how much is sanded through.  Usually a couple spratic small areas can just be spotted in. 
  • Don’t keep sanding after the body is straight and the primer is flat. 
  • There is still 220 and 400 grit to go