A climbing jack is disclosed, wherein the jack comprises a jack column, and two climbing jack sections, connected by a hydraulic cylinder or a pair of hydraulic cylinders. The jack sections climb along the jack column in a crab-style fashion. Each jack section has at least one pawl which has an axle which extends substantially transversely of the longitudinal axis of the jack column. The pawl has two ends which are adapted by being pivoted about the pawl axle to move either end into biased contact with the jack column, and to thereby engage receiving apertures or projections along the jack column. The pawl ends are biased by opposed biasing springs which selectively bias either one of the ends of the pawl towards the jack column.The climbing jack of the present invention is particularly suited for use in apparatus for progressively constructing a wall of cementitious material, wherein the jack column is periodically raised with respect to the jack sections, and wherein during alternate periods of time, the jack sections are raised along the jack column, thereby raising formwork sections attached to the jack sections.