An apparatus is provided for use in producing shell molds particularly suited to stack molding operations. In one embodiment, there is provided an electrically heated pressure plate which is arranged above the pattern frame so that it can be lowered by means of a pneumatic cylinder to compact and cure granular material treated with a bonding agent, such as resin coated sand, in the core box. In another embodiment in which the apparatus is used to make hollow shell molds, the heater plate above the core box is replaced by an electrically heated or gas heated hood. In this arrangement, the pattern frame is hinged so that it can be inverted to remove surplus sand from the pattern frame, after which the heated hood is lowered by means of a pneumatic cylinder to a position over the pattern frame to cure the back of the shell mold. The resulting cured sand molds are ready for immediate use in stack molding without further handling.