The guide rig for casting moulds comprises a moulding point (16) at which mortar from a mixing machine is poured into the casting moulds. There is also a mould removal point (8), at which the set porous concrete blocks (6) are separated from their moulds and sent for further processing. The casting point and the mould removal point are adjacent to each other. The moulds are moved on annular closed tracks (10) which extends from the moulding point to the mould removal point. There is also a short section of track leading from the mould removal point back to the moulding point.
