I am having problems with bubbles in my final coat of varnish. The shop is at room temperature so I don't think that's the problem. I use a foam brush and am able to tip-off most of the bubbles, but the tiny ones persist in remaining. The only thing I haven't done is to thin the varnish. Will that help, and if so, to what proportions should it be thinned? (I am using a spar varnish made by Benjamin Moore)