A coating slip is applied to a first surface (SA) of a moving paper or board web using a gravity-based application method, the web's (W) direction of travel is turned by 120-200°, then a coating slip is applied to a second surface (SB) of the web using a gravity-based application method, and both sides (SA, SB) of the web are dried. The coating applicators include application beams (11, 16), which are located above the web and which have a supply gap or supply holes to pour out the coating slip with the aid of gravity on to the surface to be coated. At the run of the web (W) remaining in between these application beams (11, 16) turning devices (22) are fitted for changing the web's direction of travel by 120-200° after coating slip has been applied to the first surface (SA) of the web