Catalagzi fly ash was mixed with a binding material bentonite, at 5 to 30% by weight, to obtain less permeable (k<1.00x10(-7) cm/s) liner material that may be used for waste disposal areas. For this purpose, the prepared mixtures were compacted at optimum moisture content and maximum dry density and their permeabilities were determined. It was found that 20% bentonite-Catalagzi fly ash mixture may be used as liner or cover at waste disposal areas. In addition, to see the effects of possible leachate from waste disposal areas on the permeability of the prepared mixtures, the experiments were conducted with moderately basic (20% solution of NaOH) and moderately acidic (20% solution of HCl) liquids as well. In this context, it was observed that the long-term (up to 150 days) permeability slightly increased with time. Furthermore, additional laboratory tests, such as unconfined compression tests, unconsolidated-undrained (UU) and consolidated-undrained (CU) triaxial tests, indirect tensile tests and consolidation tests, were conducted, and collapse potentials were also investigated to provide geotechnical parameters to be used in the design of liners at waste disposal areas.