Clays are porous materials and planned to be used as barrier material in radioactive waste repositories. In this context understanding of water and solute diffusion on different time and length scales is of interest. With this proposal we aim to study Na ion diffusion in clays at the atomic level, where experimental data is completely missing.Our team has previously developed a novel mu+SR method at ISIS to study ion-dynamics in solids, and we are confident to be able to use the same technique also for the current topic. For this we are applying in total for 5 days of beamtime using either the EMU or MUSR spectrometer of ISIS.