A monolithic thermocasting system for thermocasting polymer and solid material and method of use having an internal frame system; an external frame system disposed external to the internal frame system; a mold cavity formed between the internal frame system and the external frame system, the mold cavity sized to receive the polymer and solid material and shaped to form an architectural member; a duct; and a heater element disposed in the duct for outputting thermal energy to the mold cavity to heat the polymer and solid material, the thermal energy being sufficient to thermocast the polymer and solid material to a combined building material.