the for sure way to find out is mix up a small amount and see if it hardens
OK.
After mixing the mud, put it on something nonporous so it doesn't get dried
too quickly.
If the mix was bad, the next day you'll be able to smash the lump quite
easily with a moderate squeeze of your fingers.
bill

wrote in message
oups.com...
I've had an opened bag of mortar in my garage for about a month. I did
a small repair back then and only used a few scoops of it. I have a
rag covering the opening and the mortar is still powdery. Can I still
use it, or should I throw it away?

Mike