Describes a cathode assembly for electrolytic cells, e.g., chlor-alkali electrolytic cells, comprising a foraminous cathode substrate, a deposited erodible mat comprising synthetic (man-made) fibers, e.g., polyamide (nylon) fibers, on the foraminous surface of said cathode substrate, and a synthetic diaphragm on said erodible mat. Also described is a method for preparing the cathode assembly that comprises depositing a mat of erodible synthetic fibers on the active surface of the foraminous cathode, e.g., by drawing an aqueous slurry of the erodible synthetic fibers through the foraminous cathode, and subsequently forming, e.g., by vacuum deposition, a synthetic diaphragm on the erodible mat.