Bentonite clay consists of two types of materials, small nanoscale smectite particles and larger accessory material particles. When used as a barrier, it is important that as little material as possible is lost. This loss may occur if water with low salinity passes by the bentonite clay. First, the clay will swell and then the smectite particles can solubilize. This study investigates under which circumstances the material can form a filter cake of the accessory material and slow down or stop the penetration of smectite through the filter cake. It has been shown that it is possible to form such a filter cake and that the filter cake can be further improved by adding other particles.