I found a couple of bags of cement leftover from last year. They were stored in an unheated barn for almost 12 months. Is this cement too old to use for making sculptures?

The power cement is usually best within 1 year of manufacture. Although it can still be good for a while after that.. so I suggest testing it. When it goes bad it starts to form hard clumps in the bag, or takes longer to set. I would suggest taking some of the mix and make a sample piece, and watch how long it takes to set, and check how strong the sample is after a few days. The age of your bags is on the boderline, but this test should give a much better idea.

Thanks possum.