Buffing is especially valuable for dealing with the nasty side of waterbased urethane – the brush strokes, the bubbles and the less-than-smooth results many people struggle with. Buffing and Polishing Polyurethane Suggestions for buffing a poly finish to a high gloss. I was told using 800 grit, followed by 1000 grit, and then followed by hard and soft polish (auto polish - with a buffer) will give a the required mirror finish. Question (WOODWEB Member) : Has anyone tried wet sanding with Naphta on a polyurthane surface? October 19, 2013. Buffing can create a glass-smooth finish, even after polyurethane has been applied not-too-well with nothing more than a brush in an ordinary home workshop.