Is wood movement due to the changes in humidity outside of the wood? If so, does this mean that sealers and finishes are not able to keep it out?
Andy Rae: Yes, and yes.
Richard Jones: Yes. Wood is hygroscopic, meaning it takes on and gives up moisture. Film-forming finishes slow down the ingress and egress of water vapor at a molecular level, but cannot eliminate it entirely.
Kevin Hancock: This ability to allow moisture vapor to come and go can be seen as a good feature when you accept the fact that somehow moisture will make it into the wood. If it can’t escape through the finish, it will eventually cause the finish to peel.