Abstract: An extruder for the manufacture of concrete slabs, particulary hollow slabs, in a movable relationship with a casting mold. The extruder includes a feed hopper, at least one feeder, particularly an auger for generating internal pressure in the cast concrete, and at least one core member for generating a desired slab cross-section. The extruder in accordance with the invention has an assembly of at least one contoured core section which performs a combined movement of oscillatory rotation and longitudinal reciprocation to generate inside the molding space a compacting shear action in the concrete mix. The extruder in accordance with the invention is especially applicable for the production of profiled concrete objects with elongated shape at low noise and vibration levels.