Hi guys. Im new to this forum. Builder from the netherlands.
To reply on the question, my experience with the problem is that when the 2k urethane is old ( more than 2 weeks after opening new bottles) more air is produce when the blank is cured. Thats why I always buy small packages and pour a freshly openened bottle as fast as possible.
Hope this will help you solving this problem.
Best regards, Armatus