Start with 100

When block sanding polyester primer, 100 grit on True Blox is the perfect way to start sanding. Why?

  • Polyester is a hard surface to sand, usually with a heavier texture than other primers. 
  • That hard surface requires a sharp sandpaper to get it leveled flat. 
  • Anything finer than 100 grit follows the texture too much, and doesn’t cut it flat enough, leaving it with a slight ripple, rather than truly flat.  Smooth is not the same as flat. 
  • The hard surface of True Blox doesn’t allow the sandpaper to follow the texture of the primer, allowing the sandpaper to cut the texture flat. 
  • 80 grit also cuts polyester flat, but it leaves a deeper scratch, creating additional sanding steps. 

Don’t be fooled by polyester. Of course it’s possible to sand it with finer sandpaper, and it will appear to be working the same. The subtle difference really starts to show up when you’re wet sanding the paint, and just can’t get it quite as flat as you’d wish. That slight ripple might be partially from the polyester not being blocked hard enough. 

If your goal is to do the best body work and paint possible, it’s all about some of the smallest details. This is one of those important details that makes a big difference. 


  • Good stuff, thanks for sharing. Polyester and Vinyl Ester primers have proven to be the most stable products for high build primer blocking. There isn’t a urethane or epoxy on the market that can match the build, cure rate, or stability.

    Bob Hollinshead
  • Polyester is not the correct products to use for any car, site it stands easy and has a high build anff Sc easy to i get panels flat, it just doesn’t have good life out of it how about the adhesions oh yeah it’s unstable h hi ow about the cracking of polyester, yeah failed as well.
    DTM primers are the way now.
    I was the one that always thought the more expensive the better until i started comparing almost every major company after being in the industry for over 4 decades i kept hearing my custom paint friends tell me you need to try Tamco o laughed said never heard of them.
    So a few years ago i was called In a panic for some sema stuff from a friend that had to much going on i was asked to clear a Harley that needed to be finished by the next day and sent, again Tamco so I’m like it’s your stuff whatever, we’ll do VW that deal i stopped using sikkens, ppg, axalta 100%
    The primer these people have is a DTA it’s sands like polyester super high build 3 colors white/grey/black
    I’ll use white mist of the time and actually throw in a little single stage i think max is 5% and every coat i do is a different color so during blocking you know where you are.
    Just my two cents.
    119.95 a kit, reducer if needed is i think 45.00 if you want to use it, add 20% reducer and you have sealer, again tinting sealer is a great way to keep the mils down on your project.


    Mike Buschman
  • After blocking the panel flat- 100 grit on polyester, what is your follow up step. More polyester blocked with finer paper or build primer.

    Dave Boyd

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