Abstract: A vertical, open-ended ingot mold assembly including a mold stool having a relieved portion machined in its base which machined relieved portion has a cavity therein produced by erosion during casting. The useful life of the mold stool is prolonged by providing a quantity of metal particles to fill the cavity and having a plate positioned over the cavity and metal particles, which plate is secured within the cavity by a ring that is within the relieved portion of the mold stool. This ring protects the periphery of the machined relieved portion from erosion during casting and also prevents the plate and metal particles from mingling with the cast metal. For each successive casting operation, the eroded cavity is filled with metal particles and a new plate is positioned thereover. Alternately, the use of metal particles may be avoided by using only a plate of a thickness sufficient to protect the remainder of the mold stool from erosion.