A universal reusable system (10) is provided for molding concrete or other settable fluids for use in building construction. In the subject system, apertured composite plastic panels (12, 12') and frames, prestressed by the presence of an array of removable and interchangeable oversized plastic plugs (92), are positioned and held in place by a framing system which utilizes a combination of apertured strips (18, 22) used as base guides and both vertical and horizontal channels (14, 16), as well as dowels and plugs (62, 72). The use of apertured panels (12) and framing system provides for a reusable assembly whose dimensions can be readily set on site for each application and whose rectilinearity is maintained either by the dowel-aperture combination or by a combination of oversized plugs (92) in adjacent members to be joined and connectors (60, 70) therebetween.