You could spray this with layers of gunnite and build up a sealed concrete bubble. I think it'd be just as stable as an inflated form. Once you had an 'eggshell

You could spray this with layers of gunnite and build up a sealed concrete bubble. I think it'd be just as stable as an inflated form. Once you had an 'eggshell' layer of concrete, that would bear the weight of successive layers. Might require taping over the edges of the 'shingles'.