Bentonite clay consists of two types of materials; the small nanoscale smectite particles and the larger accessory material particles. When used as a barrier, it is important that no material is lost. This might occur if water with low salinity is passing by the bentonite clay. First, the clay will first swell and then the smectite particles can be solubilised. This work 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. We have showed that it is possible to form such a filter cake and that the filter cake can be further improved by adding other particles.