I'm installing a oakwood tongue& groove floor. I am attempting to use minwax spar polyurethane to seal the floors for that basketball court look. I am using a minwax polyurethane brush, I am not shaking the can, I am stirring gently, have presanded with 220 grit sandpaper and I am getting a terrible finish. I have lots of small bubbles in the finish that sanding with a 600 grit does not take out. Any suggestions or help would be appreciated.