Cover and bottom liners at waste disposal sites are usually composed of a compacted clay layer (CCL) or a geosynthetic clay liner (GCL) overlain by a geomembrane. Employing local materials in the compacted layer should be attempted, since transportation costs and environmental impacts associated to borrow pit exploitation may be significantly reduced. Saprolitic silty soils of acidic rocks, which occur extensively in tropical regions, may present adequate geotechnical properties when compacted and confined, but their compacted permeability is generally at least tenfold higher than the limit value of 10⁻⁹ m/s usually required for liners. Furthermore, characterization of this construction material is particularly difficult due to the occurrence of thick layers with great spatial heterogeneity relative to mechanical and hydraulic properties. This paper shows the results of an investigation on the technical feasibility of using a silty saprolitic soil of the metropolitan region of São Paulo for liner construction by means of bentonite addition and compaction at modified energy. Initially, optimum bentonite content was determined considering the mixture permeability. Compressibility, shear strength and expansibility were also determined for the natural soil and the soil-bentonite mixture. A test liner was built in a waste disposal site to consider practical construction aspects. Bentonite addition reduces soil permeability and ensures conformity to specification limits, without significantly modifying other geotechnical properties. The swelling potential of the natural soil and the mixture is a negative aspect that has to be properly addressed.