A device for applying a lane (C1, C2) of a fluid coating material to a building surface, such as to a building wall, by moving the device in contact with the building surface, said device comprising: a mouthpiece having a front end for discharge of said fluid material and a rear end with an inlet for said fluid material into said mouthpiece, a body including a handle for hand holding the device, - said handle extending from said rear end and including a conduit for supplying said fluid material to said inlet, said mouthpiece defining a contact face for said contact of said device with said building surface, characterised in said mouthpiece including two opposite side walls (51, 52), said material flowing between opposite insides of said two opposite side walls from said inlet to said front end, a top wall having at said front end a first face for defining together with said building surface a first gap defining the thickness of said lane (C1, C2) of said material applied onto said building surface by said device, and a flange portion extending along the outside of an adjacent one of said two side walls (51, 52), said flange portion having a second face for defining together with said building surface a respective further gap having a height that increases from the level of said first face towards said rear end, - said flange portion being for contacting a surface part of an adjacent lane of said material previously applied to said building surface, - an edge of each of said two side walls (51, 52) defining a respective portion of said contact face, - said two side walls (51, 52) diverging away from one another in a direction away from said rear end. a mouthpiece having a front end for discharge of said fluid material and a rear end with an inlet for said fluid material into said mouthpiece, a body including a handle for hand holding the device, - said handle extending from said rear end and including a conduit for supplying said fluid material to said inlet, - said handle extending from said rear end and including a conduit for supplying said fluid material to said inlet, said mouthpiece defining a contact face for said contact of said device with said building surface, characterised in said mouthpiece including two opposite side walls (51, 52), said material flowing between opposite insides of said two opposite side walls from said inlet to said front end, a top wall having at said front end a first face for defining together with said building surface a first gap defining the thickness of said lane (C1, C2) of said material applied onto said building surface by said device, and a flange portion extending along the outside of an adjacent one of said two side walls (51, 52), said flange portion having a second face for defining together with said building surface a respective further gap having a height that increases from the level of said first face towards said rear end, - said flange portion being for contacting a surface part of an adjacent lane of said material previously applied to said building surface, - an edge of each of said two side walls (51, 52) defining a respective portion of said contact face, - said two side walls (51, 52) diverging away from one another in a direction away from said rear end. - said flange portion being for contacting a surface part of an adjacent lane of said material previously applied to said building surface, - an edge of each of said two side walls (51, 52) defining a respective portion of said contact face, - said two side walls (51, 52) diverging away from one another in a direction away from said rear end.