Capillary filtration technology has been developed in Finland by Outokumpu Mintec Oy. Almost ten years of full scale experience of capillary filtration has shown that this type of filter is a very profitable and very economical solution to many filtration problems. The main area where capillary filters are used is in the dewatering of mineral concentrates. Both vacuum capillary as well as pressurised capillary filters are now commercially available. In the work reported here, the effect of flocculants on the capacity of Ceramec filters is studied. The filtrations were made using three copper concentrates and a laboratory-scale automatic dipping machine. During the experiments no permanent plugging of ceramic filter media was observed. On the contrary, small concentrations of non-ionic or slightly anionic flocculants increased the capacity. However, too high a concentration of flocculants caused plugging of the ceramic plates. There were also remarkable differences between the copper concentrates used and their behaviour during filtration with Ceramec filters. Storage of copper concentrates changes their zeta potential very dramatically. In addition, the type of copper sample has an effect on the capacity, Clearly better capacities were achieved using a slurry sample which was brought straight from the mine, compared with using a copper sample which was first dewatered in a mining enrichment plant. The results show that these kinds of experiments should be performed in the mineral concentration plant if very accurate results are desired. A good way to predict the capacity and the cake moisture of mineral concentrates is to perform test filtrations using small, pilot-scale capillary action filters which can be directly connected to the mineral concentration process.