A surface type structural component particularly applicable for aircraft, comprises a reinforcing grid structure of longitudinal and cross ribs made of fiber reinforced material. The grid structure is assembled from a plurality of molded box frames or cells. The modular box frames are formed on mold bodies and assembled and bonded together to form the reinforcing grid structure while still on the mold bodies. A laminated sheathing is bonded to the grid structure. Methods and apparatus including an automated assembly plant are disclosed for manufacturing the surface type structural component. The manufacturing plant includes automated handling equipment for molding the box frames on mold bodies, assembling the mold bodies and box frames into grid structures, forming and applying a laminate sheathing, curing and hardening the two-dimensional grid structure and laminate sheathing combination under heat and pressure and removing the mold bodies. A mold body comprising a plurality of releasably interconnecting members is also disclosed. The mold body center member is formed with an elongate core of metal material and at least a layer of heat expandable rubber or elastic material. The mold body work piece expands upon heating providing pressure for bonding and is subsequently removed to be reused.