A method of building up an aluminum alloy part by welding is disclosed. The method includes the steps of manually depositing a layer of aluminum alloy powder on the part in a build-up zone and welding the powder layer onto the part by laser welding. A mask having an opening of dimensions corresponding to the dimensions of the build-up zone is positioned on the part and the layer of powder is deposited on the part both in the build-up zone and overlaps onto the mask around the build-up zone. The height of the powder layer relative to the surface of the part is calibrated prior to the welding step.