The products and information you need to block sand your project like a pro are all here!

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The FAQ's Of Block Sanding

(Q) What grit sand paper should you use?

(A) This is where each primer will be slightly different. Prepping primer like our Contour Polyester Primer could go one of two ways. You could “finish” prep it in order to paint directly over it or you could treat it like body filler and simply block sand it flat and then prime over it with another material. If you’re going to be finishing it in order to paint directly over it you should use a combination of block sanding and DA sanding. You can rough out your work with 80, move to 180, 220, and then finish blocking with 320 grit. To get rid of those straight scratches you should DA sand with 400 grit. You could add another finer grit like 600 but in my experience 400 has proven itself to be fine enough to paint over with most materials. You should never wet sand polyester primer; it will absorb the moisture and could potentially cause issues down the road if it doesn’t completely evaporate before painting.

If you want to prep polyester primer in order to prime over it with another material, start block sanding with 80 to break it open and roughly knock the panel down flat and then do the majority of your blocking with 180 grit and finish with either 180 or 220 grit on a DA sander. This will give you the flat surface you need and avoid the extra work and time spent finishing with the finer grits. 2k Urethane Primer would be the next step from here.

When prepping 2K Urethane Primer it’s very similar to prepping polyester primer for paint except that you’ll skip the rougher grit steps. 320 grit is the best to use for dry block sanding 2K Urethane primer, it’s both rough enough to be able to sand quickly and fine enough to not need much more after you’re done. Once you’ve blocked your panels with 320 grit you should go over your work with 400 grit on a DA sander. Wet sanding 2K Urethane primer is best done with 400 to 600 grit wet/dry paper on a Durablock. Under most circumstances you will not need to DA sand over your work after wet sanding because wet sanding creates much finer scratches.

(Q) What are the advantages or disadvantages to using a DA Sander?

(A) Using a DA sander creates random circular scratches that are effectively finer than the same grit paper when used to block sand. A DA sander is a very important tool to use in the prepping process because it allows you to create a surface that is rough enough to allow for proper mechanical adhesion yet hide those sanding scratches in a way that they won’t be able to be seen through the paint when you’re all finished.

(Q) What is the benefit to wet sanding?

(A) Wet sanding offers a unique way to prep a panel that some people prefer over dry sanding. First, there is no dust to breathe in and we all understand the benefits of that. Wet sanding also allows you to work with finer grits more easily because the paper won’t clog with dust. The benefit there is that you can use those finer grits on a block and make straight scratches that will be easily covered by your sealer and color.

(Q) Do I need to use a sanding block?

(A) To achieve flat, smooth panels, it is recommended to always use a sanding block. Eastwood offers a variety of blocks with differing degrees of flexibility to adapt to the surface you are sanding. Always sand in an “X” pattern to avoid creating low spots or grooves. It is also recommended to use a Guide Coat when sanding body fillers and primers to identify any low spots, pits or areas that need additional work.

(Q) Why should I use Contour Polyester Primer Surfacer?

(A) Contour Polyester Primer Surfacer is literally a spray-on body filler. It is very high build, with little solvent which allows it to be stacked with minimum shrinkage. Many show car builders use spray polyester primers to get laser body panels throughout the block sanding process.