The paper describes the behavior of mixtures of highly compacted bentonite pellets. They are considered as a suitable impervious and tight barrier for nuclear waste disposal. Laboratory experiments aimed at identifying the hydraulic and mechanical properties of these mixtures are described. They are characterized by a very marked two-size pore space. The large pores and its evolution during wetting explain the rapid drop in permeability. The paper describes also the wetting rate effects, which are pronounced in these materials. These effects may be described if the usual assumption of local suction equilibrium is removed. Parameters of a double structure expansive model are determined by back-analysis of a set of suction controlled tests. Then, the measured performance of a large scale wetting test is compared with model predictions. © 2014 Taylor & Francis Group, London.