Takes some time for the wood to rot, ~3 years as Freddy says, recommend putting them on some sort of blocks or whatever to keep them off the dirt if you want them to last longer than above. No matter how well you try to cover them, if stored outside, you may get a small amount of condensation in the coal, the Blashak bags do have preforations in them, this has been discussed in other threads, Not a big deal for hand fed through with stokers using rice coal, some parts of a stoker can rust if the coal is placed in the stoker wet. You can always dry the coal first in some sort of bin system. Many on this site know more than me about this sort of thing. Good luck with coal, the neighbors will semi-hate you.