This is probably a silly question but does ready mix joint compund have a shelf life? I seem to remember reading about that at some time, probably in FHB. I ask because I generally like to buy the 5 gal. size for my projects, but may have several months between uses. When I seal it up i add a thin layer of water to the top followed by a sheet of saran wrap which I press in to the compound. This keeps it from drying out but I wonder if there are any other performance issues.