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I recently put together a stationary combination work bench and cabinets out of 5/8 particle board and 9/8 "benchtop" (which appears to just be thick particle board). I previously made a work table from the same "benchtop" and applied an oil-based polyurethane finish to it without issue. However I had some water-based polyurethane around that I wanted to use up, both in matte and satin finish, so I applied a coat of the water-based matte finish to my new tops.

To my surprise, the smooth face of the particle board became quite rough. Can I treat this like regular wood and just sand it back down before applying another coat of the water-based polyurethane, or do I need to try something else for my next coat?

The rough look of this combination work bench and cabinet is in this shot of the plans below, although I made a number of small changes on the fly and haven't updated the plans to match. The purple bits are intended to be slide-out drawers, and the teal bits are intended to be slide out shelves (that I'll probably mount at mixed heights), but I haven't built either of those yet.

combination work bench and cabinet

Again, my question is about re-smoothing the "benchtop" particle board that the water-based polyurethane seems to have raised, whether another coat will cause more problems after I do so. (Or if I need to just cover it with a layer of hardboard.)

Also, I'm thinking of priming and possibly painting the rest of this cabinet; do I have to worry about raising the "grain" there?

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  • In hindsight: I think it works just fine to use water-based poly if you first apply water to the surface with like a cloth, and let it dry all the way (wait like 24 hours). Then you just sand and apply the water-based poly, and the grain shouldn't rise again.
    – CRABOLO
    Commented Jun 15, 2015 at 7:52

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Can I treat this like regular wood and just sand it back down before applying another coat of the water-based polyurethane

Yes.

The finish swelled the wood fibres in the particleboard/chipboard. So although it's not raising the grain as in the case of solid wood (or the surface of plywood) it is the same thing effectively.

Don't sand too heavily. Just as when sanding raised grain on wood or ply the idea it just to smooth off the raised fibres, not to sand the surface off. So use fine paper (150-240 grit) and sand minimally, with light pressure.

Also, I'm thinking of priming and possibly painting the rest of this cabinet; do I have to worry about raising the "grain" there?

Only if using waterbased primer.

Even at that, some products raise grain much less than others. This is partly dependent on water content (higher solids content means less water) but also on other aspects of formulation.

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You could probably go through a few cycles of sanding/water-based finish and eventually get a flat and sealed surface, but if it was me, I'd sand flat and apply an oil-based primer (and follow with paint). If you must have a clear finish, sand more aggressively and use an oil based varnish-type finish.

Water based finishes will always do what you've described to particle board, so should be avoided.

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  • I expected varnish to better match my use - I was a little worried about a paint surface chipping down the road - but you expect a painted work surface would be plenty durable?
    – Michael Urman
    Commented Jun 14, 2015 at 14:32
  • I'd think that if a painted finish would look okay for you, it would be plenty durable. I'd go for a glossy (or near) finish, for easier cleanup.
    – Aloysius Defenestrate
    Commented Jun 15, 2015 at 4:06

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