Abstract: A gypsum slurry mixer includes a stationary part delimiting a mixing chamber including an upper part with a supply orifice, a lower part, a lateral part with an outlet orifice defining on the lateral part two end points and the outlet orifice is located within the angular sector formed by the centre of the stationary part and by the 2 points; a smooth movable part having an axis of rotation arranged in the stationary part; and an outlet system including a tubular element oriented tangentially to the stationary part along an axis of which the projection in a plane perpendicular to the axis of rotation is located within the sector formed by the acute angle between the projections, in the perpendicular plane, of the two tangents to the lateral part passing through the end points; and a collecting element.