In addition to the obvious requirements of being relatively inert to the molten metal being cast, and ease of prime coat shell removal, an optimal prime coat should have a balance of several factors including:

• Slurry rheology so that operators (and robots) are able to produce a uniform coating on all wax surfaces including edges. This includes adequate working time to accomplish draining of the slurry.

• Proper wetting of the wax by the slurry

• Adherence of dried slurry to the wax

• Stucco bonding

• Green permeability for ease of de-wax

• Hot permeability of the prime coating for ease of filling thin sections of the casting with metal

The effects of polymer, fiber, and carbon additions, as well as particle size distribution of the flour, in a zircon/fused silica prime slurry were studied to determine how each affected the properties mentioned. An improved slurry for first dips was the result of this work.