Ok since i saw this yesterday I have grown fascinated and gone on a deep dive. First of all, Kim Beaton invented that concrete-and-rubber-fibers stuff she mentions. It is called Pal Tiya Premium, and there is a whole youtube channel with all the information about how to mix it and use it. https://www.youtube.com/@PalTiya She makes a giant sculpture of The Great A'Tuin and Discworld with it!!!
Secondly, it cures in air alone, no oven or kiln required, and unlike clay it has microscopic shrinkage between wet and dry, so you can pack it around glass or whatever. When she says you can stand on this stuff, yes, you can (though for very large sculptures or very narrow sections of a sculpture, she recommends adding a metal armature for extra strength). It is impervious to water, so it can go outside in any weather, and any metal armature encased inside it won't rust
Additionally, Pal Tiya Premium can be added to at any point in the curing process, even weeks or months later, so you can make a sculpture in several pieces and, like with a mold, remove the foil core you sculpted on so you can use it again and again (though you have to add a sacrificial layer of foil between the core foil-sculpture and the Pal Tiya (see the videos on the youtube channel about it). You can color it with oxides, concrete stain, inks, or acrylics, including exterior-grade house paint so your sculptures can go outside.
Holy crap. My only question now is what am I going to make with this stuff, what do i need to have in my garden, aaaaaaa
