Why did polyurethane make wood feel coarse?

Question

I have a piece of pine I want to use for shelving. I added some finish and then added a thin layer Minwax Fast-drying Polyurethane (clear semi-gloss) with a foam brush. It looks great, but the wood now has a coarse texture to it.

I've never done this before so I'm guessing I screwed up somewhere or am using a bad brand of polyurethane... or maybe just need to apply more coats.

Answer 1

First of all, I'm assuming you already sanded the surface smooth enough before you started. If you put polyurethane on a rough surface you will get a rough finish.

Second, as @keshlam says, make sure there is no dust at all on the surface before you apply the finish. A slightly damp cloth can help pick up anything remaining (but make sure the wood is dry before you apply). Also, don't bother trying to apply a finish in a dusty environment, that's just asking for frustration.

Another possibility is that you kept brushing over the finish as it dried, which is a common beginner mistake. Moving quickly, do a thin coat over the surface and then don't go back to touch it up. Small bubbles may form on the surface as air comes out but it will be OK. If you keep re-brushing over the finish as it gets tacky you will leave the surface rough.

Finally, your chosen brand (Minwax) is perfectly fine, so no particular concerns there. If the can has been sitting a while make sure you stir it before using, but don't shake. You don't want to introduce unnecessary air into the poly.

Answer 2

The first coat of finish will raise the grain of the wood, so you need to sand it down with some sandpaper (220 grit or so) before you put on the next coat.

This is mentioned in the directions.

Answer 3

In addition to the excellent advice above, for soft woods like pine it is often necessary to raise the grain before applying a finish for smoothest results.

1. Sand smooth and using a tack cloth to remove the dust
2. lightly spray the surface with a little water from a spray bottle, and/or wipe the surface with a damp cloth. Don't soak the surface, just damp.
3. Let stand for a while (a few hours to overnight, depends on ambient humidity). When you come back to the wood, the surface may feel fuzzy as the individual wood fibers swell and stand proud of the surface.
4. Now knock it back down to flat with a very fine sandpaper and tack it again. Let dry, and apply your finish.

On rare occasions you'll need to do this more than once.