“A gypsum-based embedding material” is provided with which favorable casting can be conducted not only in the case where a conventional wax pattern is used, but also, in particular, in the case where a resin pattern different from the conventional wax pattern in disappearance temperature and disappearance behavior is used, and with which, although being a “gypsum-based embedding material”, occurrence of cracks, breakage, or the like in a mold is suppressed even when casting is conducted by “rapid heating” excellent in treatment efficiency. The gypsum-based embedding material composition for casting comprising, as main components, calcined gypsum as a binder, cristobalite and quartz as heat-expandable refractory materials, and a non-heat-expandable refractory material having an average particle diameter of 5 to 20 μm, the blending amount of the non-heat-expandable refractory material in 100 parts by mass of the main components being 10 to 25 parts by mass.本發明提供一種「石膏系包膜材」,其尤其是於使用有先前之蠟模型之情形時可實現良好之鑄造,而且於使用有消失溫度或消失行為與蠟模型不同之樹脂模型之情形時亦可進行良好之鑄造,進而,雖為「石膏系包膜材」,但於藉由其處理效率優異之「急速加熱」進行鑄造之情形時,亦抑制鑄模之龜裂或破裂等之產生。本發明之石膏系鑄造用包膜材組成物之特徵在於:其係以作為結合材料之煅石膏、作為熱膨脹性耐火材料之白矽石及石英、以及平均粒徑為5~20μm之非熱膨脹性耐火材料為主成分而成,且該主成分100質量份中之非熱膨脹性耐火材料之調配量為10~25質量份。
