A direct mold includes a plank frame and a mold surface body held in shape by the plank frame. The plank frame is made of a plurality of planar panels that are aligned transversely to the longitudinal extension of the rotor blade and are arranged spaced with respect to each other in the direction of the longitudinal extension of the rotor blade. The panels of the plank frame have recesses, into which the mold surface body is inserted and which reproduces in its sequence in the plank frame mainly a progression of a contour of a part of a rotor blade profile. The mold surface body has a layer structure that includes a support layer and a sandwich layer. The support layer is made of rails that are aligned in the longitudinal direction of the rotor blade in a manner bridging the distances between the panels.