This problem comes up a lot at this time of year. You’ve been finishing a large project for several weeks without problems. Then the finish starts sagging on vertical surfaces and the cabinet doors begin sticking together
when you stack them.
It’s important to remember that all finishes dry slower in lower temperatures. Unless you keep your shop heated (and cooled in summer) to a fixed temperature, you’re likely to experience some of these problems as winter approaches.
To avoid runs and sags, watch the finish in a reflected light as you’re applying it. The reflection allows you to see if either of these problems is developing and you can brush them out to remove them (even if you’re spraying). If you are spraying you’ll also learn to spray thinner coats, and if you’re brushing you’ll learn to brush the finish out thinner.
Pressmarks occur when something is pressed up against a finish that hasn’t fully hardened. The only thing you can do to remove the damage is sand it out, after the finish has hardened enough to sand, and apply more finish.
To prevent more pressmarking warm your finishing area or give the finish more time to harden, or both.
– Bob Flexner