I just learned the hard way that plaster cloth, such as that made by Woodland Scenics, absorbs water from the air over time. Two opened packages stored on a shelf in my shed were totally useless when I tried them today. A sealed, unopened package stored right next to them was perfectly fine. From now on I'm going to keep opened packages in air-tight freezer bags. -Dave
Yah - same goes for open bags of plaster...and most everything else that kicks with water (urethanes are the expensive ones which I have learned hard on).
I picked up one of those vacuum sealers that they make for storing food and what not on sale a few years back for pretty cheap. Now, when I get done with a project, if I have any material left over I put it in one of the bags and vacuum it down and reseal it.