In recent years, because of the continuous expansion of urban areas, an increased necessity to isolate historically polluted sites by means of artificial, flexible, low-permeability barriers has emerged. Moreover, due to cost and efficiency considerations, various combinations of materials that fulfill the previously stated requirements have been proposed. On the basis of a literature review, this paper analyses the relationships between water, cement, and bentonite, and the physical and mechanical properties of the resulting material created in combination with standard sand introduced in the mixture using a ratio of 2:1 with respect to the solid part of the mixture (cement and bentonite). The quantity of standard sand was established following previous research conducted by the authors. The relation between water, cement, and bentonite is analyzed through properties such as viscosity, permeability, and undrained cohesion, and the representation of mixtures and their corresponding parameters was carried out using a ternary diagram. This paper provides a graphical approach to finding the optimum water/bentonite/cement mixture required for barrier design, taking into account permeability, undrained cohesion, and mixture viscosity.