Prototype Aluminum Casting Methods Our prototypes are made either by the plaster or air-set sand process. The type of casting dictates the method that we use, unless specified by our customer. The plaster process is used when fine detail and finish are essential. Thin wall castings can also be cast with this method. Walls down to .060" can be cast. Rubber patterns can be used when making plaster molds. When using rubber patterns, minimal or no draft is needed, facilitating a cast to print part. Cast to size castings help to cut down machining costs. Also, with rubber tooling, minimal parting compound is required thus insuring more detail. With plaster molds, porosity can be a problem. We've nearly eliminated porosity using a rotary degassing.