Hypertufa pot is stuck in the mold (a metal pot)

I wonder does anyone have an idea I haven't thought of on how to coax it out? I used a large enameled spaghetti pot as a mold, and thought a little oil and a plastic bag would be enough to line it with. The pot has straight sides, so it's not a matter of it being wider at the bottom. I think I just compacted the hypertufa so well that pressure is keeping it in. I am resigned to breaking up the hypertufa and throwing it out, as the cooking pot is the more valuable item, but this question is my last ditch effort to save my work.

In attempts to break the tight seal, I've tried tapping the sides of the pot with a hammer; pouring in more oil between pot & hypertufa; pouring a laundry detergent solution in. Has anyone ever faced my problem?