Abstract: A method of casting concrete structures using a "flexible formwork assembly". The assembly has flexible sheets suspended from a fixed location, preferably from a supporting frame assembled on top of the reinforcing members, with rigid stress distribution members located to the outer surface of flexible sheets in predetermined spacings so as to carry load directly and to redistribute stress in the sheet so as to aid the sheet to withstand the concrete pressure. The majority of stress distribution members are arranged in pairs which are directly connected to each other by ties in wall type structures. Reinforcing members are used as a main frame or skeleton to hold and suspend the formwork assembly. Spacers are used to aid in maintaining the sheets in a desired location which ensure adequate concrete cover to the reinforcing prior to pouring of the concrete. Stress distribution members provide external shape, configuration and pattern to the concrete surface by their shape and arrangement.