As the title suggests, I'm looking for alternative ways to go about doing the fake rock structures. From what I've seen, most people use styrofoam to create the bulk of the structure, expending foam to fill in, then level out with grout before painting and sealing. While I wouldn't use this, I came across a clay substrate and was wondering if there's smth like so that would be okay to use? Obviously any necessary precautions would be taken as I would with sealing the structures made from foam.