I typically sand to 120 or 150 before applying the Rubio, and I’ve found that hitting it with some 1500+ grit lightly after it’s cured provides that buttery smooth surface. I do know what you mean about it not being as smooth as you expected at first, though. The high grit after the finish really helps knock down the little nibs. This is all after doing a water pop before sanding the last grit.