Report Bowl (used as model) stuck in plaster after pouring in Studio Operations and Making Work Posted 15 hours ago I had the same with an owl mould. Tried water, soap, air. Nothing shifted it. In the end we sawed the foot off, and then put it back together with dowels. It worked fine as a slip-casting mould. We never determined the problem. The master was cast-Iron, and had several coats of sealer and copious amounts of release. Maybe it just likes it's new plaster coat.