The Grits

Using the proper grits when sanding polyester primer matters.  Here are the steps, and their purpose. 
  • 100 grit. This grit is to sand the texture of the polyester primer completely flat. Of course this first step also needs to be used to continue straightening the body work. Typically, use the same sanding blocks that were used during body work. The block should take just a small amount of pressure to conform to the general shape of the panel.  Don’t use a flexible block for a flat panel, and don’t use a rigid block for a panel with shape in it.  Get your work as straight as possible in 100 grit, don’t move on to 220 until everything is straight. 
  • 220 grit is next. This step is highly important in getting your panels straight. 220 grit is where the work really gets refined, and you can work out any slight imperfections that didn’t show up in 100 grit.  The same blocks can be used, or slightly shorter or more flexible blocks can be used. Make the judgement call based on the project. 
  • 400 grit is the final step.  This step isn’t meant to straighten any body work.  This step is only to get the sand scratches fine enough and smooth enough. Don’t use True Blox in this step, use some sort of foam block, like the Style line soft sanders, or a pool noodle material.  Everything needs to be smoothed and softened in 400. 
  • There are cloth sandpapers now available in a range of grits, they work great wrapped around a soft block. Use somewhere around 600 grit dry. It’s an excellent finish prior to sealer. 

Of course, use plenty of dry guide coat between each of these steps.