(57) An apparatus for manufacturing a building block is of the type having a mould box (1), and at least one core (3) rigidly mounted in the mould box by means of a spacer bar (4). At least a portion of the moulding surface of the core and/or the mould box is formed from a rubbery polymer. The polymer may be used as a coating (8) and/or the core (3) may be a moulding of the polymer. An undercut may be made in a block by providing a core (16) with an expandable resilient portion. The polymer may also be used to provide a cushion (8) under the lower edge of the mould box (1).
In the process using the apparatus the mould box (1) and core (3) are removed from uncured mould blocks after a very short time e.g. 1 to 60 seconds.