What Is the Best Way to Sand Before Applying a Waterbased Stain or Finish?
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Q: Recently I built a bassinet using oak. When it came time to finish the wood, I used a waterbased polyurethane, and the grain kept popping out. I would sand off the rough stuff and apply the next coat. This kept happening over and over until I gave up on a few rough spots. Is there a better approach?

Proper pre-finish sanding To get the most out of your finish, make sure you sand down to a nice, even grain across the whole board.

A: Absolutely. It sounds as if you were trying to do the right thing in the wrong way. If you plan to use waterbased coatings or stains, your best bet is to raise the grain of the wood first, before any finish is applied. Once it is raised and leveled, it will not raise again. However, it must be done the right way or you will end up, as you did, chasing your tail. It all hinges on getting enough water into the wood initially and using the right sanding method and materials afterwards.

After sanding your wood to the last grit you normally use, which for me is usually 180-grit garnet paper, wet the raw wood thoroughly with clean water. Don’t wipe it with a damp rag; soak it thoroughly with a sponge, then wipe off all the standing water. The wood surface will be saturated but with no standing water or puddles left. Now let it dry overnight.

The next day, when the wood is completely dry, it will feel furry, with raised grain all over. That’s because sanding leaves the ends of wood fibers shredded, and water makes them stand up. Cut back the raised grain by sanding very quickly and lightly with fine paper. I usually use 400-grit.

The object here is the same as when you shave: you want to remove the raised hairs, but you do not want to cut into the wood (or skin) below. Sand only enough to smooth the raised fibers. If you sand too aggressively or use too coarse a paper you will simply shred the wood anew, and the newly shredded wood will then raise when it comes in contact with water. Raise the grain and smooth it right the first time, and you won’t have to do it again.

posted on April 1, 2008 by Michael Dresdner
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