Ihave a bottle on my bench that is two years old and still working like new. I live in a no moisture climate though so that may have something to do with it.
When I use it Igo out to my shop about every hour and with a damp rag Iwipe off the expansion, after a while it has quit expanding. Not sure about sanding it though, I only use it for a few things these days. Very good stuff and very strong, just a pain to use sometimes.