Treatment of wastes became a vital demand to maintain the environment as clean as possible . The treatment of wastes and reuse of their constituents in industry will be helpful for this trend as well as for economy. Flotation technique is one of the important separation techniques that can be applied for treatment of wastes efficiently. The filter cake of El-Maghara coal washing plant was one of these wastes which contains a considerable amount of clay. This filter cake was treated in a previous work by flotation in order to clean it from the contained fine coal. The residual clay was tested as a raw material to produce brick models with acceptable mechanical properties. Improvement of the mechanical properties of such brick models by mixing such clay with sand is exactly the main objective of this work. The effect of different factors such as, weight percent of sand and its particle size on the mechanical properties of the brick models was investigated. It was found that 20 % and 60 % of sand sample characterized by size distribution of - 1500 + 0 μm and - 500 + 0 μm respectively are enough to achieve a considerable extent of improvement in the mechanical properties of the clay brick produced.