Assembly of the ski is effected in one preliminary step in which a mechanical resistance sub-assembly is produced, followed by a single molding step. During the preliminary step, at least one lower reinforcement piece (1), a core (2), and an upper reinforcement piece (3) are stacked together, said stacked assembly is inserted in a heat retractable casing (4), and the casing is heated to shrink it retracted. During the single molding step, the lower elements of the ski structure (11, 12, 13) are placed in the mold, the mechanical resistance sub-assembly is placed on the lower elements of the ski structure, the mold is closed, and a thermohardenable polymer is injected so as to form the protective covering (15) of the ski.