We installed a tongue and groove pine ceiling, and for 3 yrs we had 1. Coat of sealer on it, and it started to look really dry, so we pu several coats of varathyne on it. And now we are hearing loud cracking, and a in a few boards it has pulled the tongue and groove apart, what is wrong. We have electric heat. We have had this ceiling for 4yrs, and had no problem, what do you suggest