I’m using satin polyurethane thinned with about 10% mineral spirits. I find that the varnish is drying with brush marks still showing. I’m using a good quality bristle brush, flowing it on, then tipping it along the grain. I suspect the problem may be related to the recent hot humid weather; even though I wait 24 hours before recoating, it’s possible that the previous coat has not cured enough. Would this accelerate setting of the new coat enough to cause drying before the brush marks level out?
Thanks for any help understanding this problem.