Rapid technique for making improved laminar ceramic shell molds using a phosphate modified aluminum salt binder

A process for rapidly forming a laminar ceramic shell mold on a supporting structure comprising alternately, in either order, the steps of: (1) dipping the support structure into a bath comprising either an alkali stabilized solution of ionic silicate or an alkali stabilized solution of colloidal silica to define a first coating on the support structure; and (2) dipping the support structure into a bath comprising an acid stabilized solution of phosphate modified aluminum salt to define a second coating on the support structure. The coatings on the support structure react to form a gel set shell which can be fired to a ceramic material. The dipping step sequence is repeated to provide additional coatings which react to define additional layers of gel set shell. The rate of laminate thickness buildup can be increased by including fine particulate refractory in the coating baths and the coated surface can be contacted by dry, relatively coarse refractory to define a stucco layer between the dip coatings. The chemically induced gel set eliminates the need for air drying between coating applications thereby saving a major portion of the total process time. When the laminar refractory is formed around a disposable wax pattern of a desired metal shape it produces a strong ceramic shell mold that fully meets the requirements for the precision casting of metals.