Recycled applications were investigated for an ash produced from the incineration of diatomaceous earth filter cake used in the manufacture of additives for petroleum products. A complete chemical and physical characterization of the ash was conducted. It includes lumps which are the result of gypsum cementation. The ash produces light-weight products and exhibits pozzolanic characteristics. Mixtures of the ash with sand and other stabilizing agents were investigated for road base and subbase applications. Strength and durability tests and a microanalysis were conducted to identify the stabilization products produced. The testing program for this study indicates that the ash holds promise as a light-weight fine aggregate for use as an earth fill material.