The present disclosure relates to an apparatus (1) for forming a mould cavity (4) to form a wall section (2) of a cast-in-place wall. The apparatus (1) includes a plurality of forming plates (5-n) for forming a support wall (6) which defines at least one wall of the mould cavity (4). A support assembly (7) is provided for supporting the forming plates (5-n). The forming plates (5-n) are configured to be assembled into a first row (R 1 ) for forming the mould cavity (4) for a first concrete pouring operation. The forming plates (5-n) are configured to be assembled into a second row (R2) forming the mould cavity (4) for a second concrete pouring operation. The present disclosure relates to a corresponding method of forming a wall section (2) of a cast-in-place wall.