System for applying a building material, the system comprising: a movement device for changing an application site in a space; a first component of the building material; a second component of the building material; and a mixer for mixing the first component and the second component, wherein the mixer comprises a drive and a mixing chamber with an agitating shaft and a conveying device, wherein the conveying device is configured as a screw conveyor with windings (10, 10.1, 10.2, 10.3, 10.4, 10.5); - wherein the building material contains fibres, and: o a distance (13.1, 13.2) between adjacent windings (10.1, 10.2, 10.3) of the screw conveyor is at least 40% of a length of the fibres, and/or o a distance between adjacent agitating elements of the agitating shaft is at least 40% of a length of the fibres; or - wherein the building material does not contain fibres, and: ∘ distances (13.1, 13.2, 13.3, 13.4) between adjacent windings (10.1, 10.2, 10.3, 10.4, 10.5) of the screw conveyor are smaller, the closer the windings (10.1, 10.2, 10.3, 10.4, 10.5) are arranged to an outlet, and/or ∘ a distance between adjacent agitating elements of the agitating shaft is between 5 and 50 mm; or - wherein the first component contains an aggregate, and wherein a distance between ends of agitating elements of the agitating shaft and an inner wall of the mixing chamber is at least as large as a diameter of the grains of the aggregate; characterized in that the first component of the building material is a pumpable concrete, and wherein the second component of the building material comprises a concrete additive which contains an accelerating admixture. a movement device for changing an application site in a space; a first component of the building material; a second component of the building material; and a mixer for mixing the first component and the second component, wherein the mixer comprises a drive and a mixing chamber with an agitating shaft and a conveying device, wherein the conveying device is configured as a screw conveyor with windings (10, 10.1, 10.2, 10.3, 10.4, 10.5); - wherein the building material contains fibres, and: o a distance (13.1, 13.2) between adjacent windings (10.1, 10.2, 10.3) of the screw conveyor is at least 40% of a length of the fibres, and/or o a distance between adjacent agitating elements of the agitating shaft is at least 40% of a length of the fibres; or o a distance (13.1, 13.2) between adjacent windings (10.1, 10.2, 10.3) of the screw conveyor is at least 40% of a length of the fibres, and/or o a distance between adjacent agitating elements of the agitating shaft is at least 40% of a length of the fibres; or - wherein the building material does not contain fibres, and: ∘ distances (13.1, 13.2, 13.3, 13.4) between adjacent windings (10.1, 10.2, 10.3, 10.4, 10.5) of the screw conveyor are smaller, the closer the windings (10.1, 10.2, 10.3, 10.4, 10.5) are arranged to an outlet, and/or ∘ a distance between adjacent agitating elements of the agitating shaft is between 5 and 50 mm; or ∘ distances (13.1, 13.2, 13.3, 13.4) between adjacent windings (10.1, 10.2, 10.3, 10.4, 10.5) of the screw conveyor are smaller, the closer the windings (10.1, 10.2, 10.3, 10.4, 10.5) are arranged to an outlet, and/or ∘ a distance between adjacent agitating elements of the agitating shaft is between 5 and 50 mm; or - wherein the first component contains an aggregate, and wherein a distance between ends of agitating elements of the agitating shaft and an inner wall of the mixing chamber is at least as large as a diameter of the grains of the aggregate;