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 , 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 (F1) for defining together with said building surface a first gap (G1) 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 , said flange portion having a second face (F2) for defining together with said building surface a respective further gap (G2) having a height (W2) that increases from the level of said first face (F1) towards said rear end , - said flange portion being for contacting a surface part of an adjacent lane (C1) of said material previously applied to said building surface , - an edge of each of said two side walls defining a respective portion of said contact face , - said two side walls 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 , 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 (F1) for defining together with said building surface a first gap (G1) 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 , said flange portion having a second face (F2) for defining together with said building surface a respective further gap (G2) having a height (W2) that increases from the level of said first face (F1) towards said rear end , - said flange portion being for contacting a surface part of an adjacent lane (C1) of said material previously applied to said building surface , - an edge of each of said two side walls defining a respective portion of said contact face , - said two side walls 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 (C1) of said material previously applied to said building surface , - an edge of each of said two side walls defining a respective portion of said contact face , - said two side walls diverging away from one another in a direction away from said rear end . <EOS>