Capillary filtration technology has been developed in Finland by Outokumpu Mintec Oy and both vacuum capillary and pressurized capillary filters are commercially available nowadays. Almost ten years of full scale experience in capillary filtration shows that this type of filter is a very profitable and a very economical solution to many filtration problems. In this study the effect of flocculants on the capacity of Ceramec filters is studied. The filtrations were made using three copper concentrates and using a laboratory-scale automatic dipping machine. During the experiments, permanent plugging of ceramic filter media was not observed. On the contrary small concentrations of nonionic or slightly anionic flocculants increased the capacity. There were also remarkable differences between the copper concentrates used and their behaviour during the filtration with Ceramec filters. A good way to predict the capacity and the cake moisture of mineral concentrates is to do test filtration using small pilot capillary action filters from Outokumpu Mintec which can be directly connected to customers＇ processes on site.