Disclosed is a method for grinding a hydraulic binder, including: a) introducing:—a hydraulic binder, and—a composition B including at least one grinding aid B into the first chamber of a horizontal grinder including several chambers, including a first chamber and a last chamber, each chamber being separated from the adjacent chamber by a diaphragm, whereby a composition β including the hydraulic binder and composition B is obtained in the first chamber; and b) grinding composition β in the horizontal grinder, whereby composition β moves from the first chamber to the last chamber and a ground composition C is obtained at the outlet of the last chamber. At the grinding step, the method includes introducing into the last chamber a composition A including at least one grinding aid A including an aminoalcohol. Also disclosed is a corresponding grinding unit.