The invention provides novel binder, slurry and dry mix compositions for use in the production of investment casting moulds. These compositions comprise water insoluble fibers and significant amounts of uncalcined clay. The compositions display favorable separation characteristics and short drying times. The moulds formed using the compositions have a favourable green strength and conform closely to the wax pattern on which the mould is coated. Also provided are methods of producing the compositions, methods of investment casting mould production utilising the compositions and investment casting coating shells produced using the compositions of the invention.