New answers tagged polyurethane
I would go to a finer grit after the 220. Yes you need to sand until it is SMOOTH. Do you have a random orbit sander? Wipe on poly (50/50 poly and thinner) is a good way to go. The coats are thinner so you need 2 or3 more. Brushing works well but with a GOOD brush or a foam brush.
Once the urethane has dried, sanding will only fog up the surface. You could sand it to remove any large imperfections and then put on another coat. If you were getting streaks you may want to work in a slightly cooler area so it takes longer to dry and you have more time to work with it.
I would use a dual action orbital sander and wet/dry paper @1200 grit a very wet sponge to dampen the area dont press down let the sander float and as the streaks are cut out the residue will turn milky, keep wiping and moving this high grit with water will leave a mirror finish, I have used 800 & 1000 to remove larger imperfections but the 1200 works ...
Other discussions have pointed out that sanding between coats should be minimal -- just scuff-sanding for better adhesion of the next layer and to remove surface dust -- and may not be needed at all,
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