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I never have been able to apply a finish with a foam brush that it didn't make bubbles. I don't try anymore, I use a soft bristle paint brush when working poly by hand. It's hard to say how many coats to apply. Some people put enough on in one coat where others brush it on really thin. The objective with any film coating is to apply the finish about 3 mils thick (about the thickness of a lawn and leaf trash bag). It is equally important to allow enough drying time between coats. If the weather is cool where you are it may take many times the suggested drying time on the instructions. When you sand the finish between coats if the finish tends to gum up on the sandpaper it isn't near dry enough to recoat.