I'm trying to finish an old nightstand with glossy polyurethane and I keep getting bubbles in my finish. I don't shake the can and I stirred it very carefully to avoid bubbles. Some of the bubbles will pop out before the finish dries but not all. What can I do to prevent this?
When brushing on a finish some bubbles are inevitable. The trick is to get them to pop out of the surface before it starts to cure, or harden. To accomplish this you will want to try to lay on a very thin smooth coat. You can do this by "flowing" the finish on with smooth motions. Brushing with back and forth strokes like you're painting a house is just asking for bubbles.
The second trick is to thin the finish with paint thinner or mineral spirits (if you're using polyurethane). This will cause the finish to take longer to dry and allow the bubbles to pop out. The downside to this approach is that the longer a finish takes to dry the great the chances are dust will land on the surface.
Bubbles can also be caused by wood that warms as the finish cures.