Self-supporting intermediate walls (12) for cellular division of mould lower parts in a concrete casting machine of the kind typically used for making cast items in the form of concrete blocks for wall construction and elements, solid blocks or blocks with cavities or recesses in two or more rows. By the self-supporting design, the distance between rows of products may be reduced for better utilization of the production plate while at the same time maintaining the replaceability of wear parts. By the invention is indicated a self-supporting intermediate wall (12) consisting of two halves, an intermediate wall with lower pins (18) and an intermediate wall with upper pins (20) which, when the two halves are assembled with the pins engaging a partitioning plate (8), form a self-supporting intermediate wall (12). For moulds with core supports (28), intermediate wall parts (22 and 23) are used with a recess (25) in which the boss (29) on the core support iron (28) fits.