Abstract: In the casting of a concrete element, such as a column support block, in which there is used a mould core designed to produce one or more recesses or grooves in the element, the mould core is provided with one or more apertures or slots, in each of which there is arranged a recess-forming mould part which can be moved in said aperture or slot by means of a ram. Prior to a casting operation, the moveable mould part is moved to an outwardly projecting active position and, subsequent to the cast element hardening, is withdrawn by means of the ram, thereby to enable the cast element and the mould core to be separated from one another. All of the moveable core parts on one side surface of the mould core can be arranged on a plate extending parallel to the corresponding side surface of the mould core and arranged to be acted upon by the ram.