Abstract: A device for applying plugging mix to well walls comprises installed in series and interconnected a piston having passages for the flow of a fluid and spring-biased locking members for fixing the position of the device with respect to a drilling string, and a head carrying vanes for applying plugging mix to well walls and a bit for drilling-off the mix installed at the distal end of the head. The head has passages for the flow of the fluid. The vanes are made in the form of two plates installed on opposite sides of the head at an angle with respect to its axis of rotation, the vanes being radially movable with respect to the axis of rotation. The piston, the head and the bit are of a diameter which is slightly smaller than the nominal inside diameter of the drilling string.