A clamp for holding together the portions of a mold used in molding solid objects from a reacting liquid such as polyurethane has a C-shaped frame which is pivotally mounted on a pedestal to swing through an arc. The C-shaped frame of the clamp consists of an integral structure having an upper jaw connected by a column to a lower jaw. The frame supports a bed, crown and platen. The bed and crown are each a plate-like member that is mounted to pivot relative to one of the jaws. The platen is mounted preferably on the bed or lower one of such members. The mold portions are mounted on the crown and platen with the parts being arranged to move so that the mold portion engage and disengage. The invention also includes a method of molding wherein the mold portions are engaged and disengaged by a process that involves pivoting at least one and preferably both of the portions relative to the C-shaped frame.