My last polyurethane finishing experiment failed. I applied fast-drying Varathane to 3/4" maple plywood shelves. They were very finely finished before applying the polyurethane, and became very rough after. I suspect that the culprit is a combination of overzealously going over surfaces more than once and using a fast-drying formula.
It's almost springtime and I'm now about to apply polyurethane to floors (after sanding them). I've learned the two lessons (use a slow drying formula to forgive minor overcoats, and attempt not to overcoat in the first place). Of course I'll be sure to remove the last speck of wood dust before finishing.
The last potential issue is the brush. I've used a general purpose brush (similar to those one might use for painting walls). But the first comment at the link above suggests using a painting pad / sponge squares. My local store's website lists "paint edger", brushes , and of course rolls. What are painting pad / sponge squares called at the main chains' websites, and are these indeed the simplest way to get a smooth finish after one application? My objective is to apply one layer this year and repeat when necessary, since I see that even the pros do not bother with two layers so I'd also rather not.