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The conventional approach to generate pores in ceramic membranes involves the incorporation of a pore-forming element. However, this method tends to diminish the mechanical properties of the membranes and poses challenges in effectively regulating both pore size and membrane porosity. In this work, low-cost ceramic filtering membranes with enhanced mechanical strength have been successfully prepared mainly from abundant clays and without the need for pore-forming agents. The Porosity and pore size were controlled by adding a finely-grained clay (d 90 = 22 μm) by-product to coarse clay (d 90 = 50 μm) within a specified range of 33–66 wt%. The microstructure evolution of prepared membranes was examined by XRF, FTIR, XRD, SEM, and DTA-TGA analysis, while the technological properties were evaluated by permeability, porosity, density, and mechanical measurements. The findings indicated that the increase in the amount of finely grained clay mixed with coarse clay and the sintering temperature had a synergistic effect on the porosity and pore size of the obtained membranes. The incorporation of finely-grained clays, accompanied by an elevation in sintering temperature, led to a reduction in porosity from 31.3 ± 0.7 % to 6.2 ± 0.5 % and pore size, along with the crystallization of the α-mullite (12 %) and anorthite (30 %) phase with a quartz phase and an improvement in mechanical strength reaching up to 251 ± 3 MPa. A formulation comprising 33 wt% of finely-grained clay by-products and 67 wt% of coarse clay, sintered at 1000 °C, emerged as a promising ultrafiltering membrane with enhanced mechanical strength reaching 120 ± 1 MPa, and a permeability of 1000 L/h.m2 at 1 bar. [ABSTRACT FROM AUTHOR]