Sand polyurethane lightly between coats with 220- or higher-grit sandpaper. You should see a fine, white powder after sanding — if not, allow it to dry longer between coats. For the smoothest finish, wipe the surface with a sticky tack cloth before adding another coat.
Oil-based polyurethane varnish brings out the wood's natural beauty or wood grain.. NOTE: Water-based stains will need a fine sanding with 220-grit sandpaper after the stain is dry.. Let this coat dry for 24 hours, then apply the final coat.
(Skip the stain if you intend to leave your workpiece natural-color.) Let dry.. After the third coat, sand with 320-grit, then 400-, and finally 600-grit sandpaper.
While wood stains add color and bring out the beauty of the wood, clear finishes protect the wood. Then remove all the sanding dust and apply a second coat.
I am staining some spruce with Minwax Oilbased Dark Walnut Stain. I initially use wood conditioner, then I apply the stain. After 10 minutes I .