The present disclosure relates to a mold core for use on a molding apparatus for the production of hollow and/or in particular tubular concrete bodies, and a molding apparatus comprising such a mold core. The mold core comprises a longitudinally extending wall of the core, which has a wall of the core from one end to the other end of the wall of the core in the longitudinal direction, an expansion device for expanding and/or spreading and/or contracting and/or shrinking the mold core, and a sealing element sealing the longitudinal opening of the wall of the core. The sealing element is provided with respective longitudinal edges of the wall of the core by means of a detachable connection, the sealing member being slidably connected to the two longitudinal edges of the wall of the core in the longitudinal direction, respectively.