an apparatus and method for forming foundry cores and molds of superior hardness and uniformity in a wide range of sizes includes staging hoppers for storing a first mass of sand coated with a catalyst - polymerizable resin film , and a second mass of sand coated with a catalyst film for polymerizing the resin . in forming the cores or molds these masses are simultaneously and evenly dispersed into a high velocity carrier air - sand stream and directed through a static mixer , wherein the resin and catalyst - coated sand particles are intermingled and at least a partial integration of the films takes place into a shaping mold cavity , wherein the sand mixture hardens into a desired shape . for improved integration of the resin and catalyst films , and for improved core density , air is injected into the air sand stream downline of the static mixer immediately prior to the sand mixture entering the shaping mold .