The method of cellular automata for modeling heat and mass transfer in heterogeneous media with barriers is considered. It is shown that shell molds consisting of various components with heterogeneous physical and chemical properties are heterogeneous media. Mass transfer processes in the system “casting - mold” significantly affect the quality of the received casting, especially in molds of complex design. To model the influence of heat and mass transfer processes on the surface quality of castings, two-layer molds with a working layer of sand-resin mixture and a support layer of materials with different gas content, gas permeability and heat storage capacity were selected. A three-dimensional model of Stochastic Excitable Cellular Automata (SECA) was used to study the specifics of the process of heat front propagation in shell-type molds containing barriers.