Abstract: In the construction of tall concrete towers, a two part derrick is suspended by cables from the tower to the lower part of the derrick. The derrick is extended on hydraulic rams, raising its upper part and outside casting forms. A pulley system maintains a deck scaffold and inside forms at their original level during extension. Extension of the derrick slakens cables from the tower to the upper part of the derrick. These cables are disconnected from the tower and reconnected at a higher level. Outside forms are fixed, reinforcing steel set in place, and the derrick retracted, raising the deck scaffold and inside forms by the pulley system, and slacking the lower cables. The lower cables are disconnected from the tower and reconnected at a higher level. Inside forms are set and concrete is poured. The concrete sets and the procedure is repeated.The deck scaffold comprises radiating wooden beams with endpieces.