Abstract: A core form is disclosed for casting a structurally reinforced concrete structure for use on a slab with an outer container form having rigid walls extending vertically comprising a casting core positioned internal the outer form and having vertically extending resilient walls defining an within contiguous core wall. The walls of the outer form and the walls of the casting core are spaced apart to define a mold cavity therebetween. A form base supported by the slab is positioned within the mold cavity to releasingly support the concrete structure to be formed and cured within the mold cavity. The walls of the casting core include an upper and lower periphery such that in use the lower periphery abuts the form base to seal the concrete internal the mold cavity relative the periphery and form base. The internal contiguous core wall is retractable to enable the placement of the reinforcing structure within the mold cavity.