Can i use hardening clay to stick things together?
It’s a little confusing to know exactly what you want, and what materials you’re talking about. The “polymer clays” (often called oven-bake clays –brands like Fimo, Premo, Kato, Cernit, Sculpey, etc) must be heated to harden and will never dry in the air. They could be used to hold some kinds and shapes of materials together, but mostly only with a “mechanical hold” since they’re not adhesive once they’ve hardened. The “air-dry” clays (many types and brands–like Creative Paperclay, Model Magic, homemade bread clay or salt dough clay, Crayola Air Dry Clay, purchased PlayDoh, paper pulp, etc) don’t need any heat to harden; they will simply lose their water and “dry” if left out in the air to harden. They’re not adhesive on their own once dry either though. You could certainly use them instead of a polymer clay like Sculpey** but air-dry clays may shrink while drying and will also require a sealer (permanent clear finish, or acrylic paint, etc) so they won’t become soft from later humid
