Method for applying a polymerizable mastic and carrying out a coating of a rivet head emerging from a sheet using a device comprising: - a substantially cylindrical cartridge containing an activated polymerizable mastic, said cartridge having a distribution end and a pressure end; - a receptacle for said cartridge comprising a connection interface with the distribution end thereof; - pressure means acting on the pressure end of the cartridge to cause the ejection of the activated mastic through the distribution end; - a removable application assembly comprising a mastic-feed pipe in a buttoning nozzle (625, 725) which comprises a pre-filling chamber, a bell-shaped cavity able to fit on top of the rivet head, an application orifice putting the pre-filling chamber and the bell-shaped cavity in communication; - a closure needle, able to move in translation between a closed position where an end of the needle obstructs the application orifice of the nozzle (625, 725) and an open position where the end of the needle is distant from the application orifice; - means for maneuvering the needle in translation between these two positions; - automation means for sequencing the action of the pressure means and the movement of the needle between the open and closed positions; the method comprising the steps of: - a) during a positioning step, placing the nozzle (625, 725) so as to fit on top of the rivet head, the application assembly being filled with mastic, the needle being in the closed position, moving the pressure means (215, 415) so as to achieve a predetermined pressure in the feed pipe and the pre-filling chamber of the application assembly; - b) during a coating-beginning step, moving the needle into the open position so as to open the application orifice and to allow flow of the mastic in the cavity and onto the rivet head; - c) during a coating-ending step moving the needle into the closed position and stopping the flow of the mastic; - d) during a movement step, the needle remaining in the closed position, releasing the nozzle (625, 725) from the rivet head and moving the device to the following rivet head, and then resuming the cycle at step a) on said following rivet head; characterized in that, during the positioning step a), the nozzle (625, 725) is positioned above the rivet head, the end of the nozzle (625, 725) being located at a suitable distance from the sheet to enable air to escape during step b). - a substantially cylindrical cartridge containing an activated polymerizable mastic, said cartridge having a distribution end and a pressure end; - a receptacle for said cartridge comprising a connection interface with the distribution end thereof; - pressure means acting on the pressure end of the cartridge to cause the ejection of the activated mastic through the distribution end; - a removable application assembly comprising a mastic-feed pipe in a buttoning nozzle (625, 725) which comprises a pre-filling chamber, a bell-shaped cavity able to fit on top of the rivet head, an application orifice putting the pre-filling chamber and the bell-shaped cavity in communication; - a closure needle, able to move in translation between a closed position where an end of the needle obstructs the application orifice of the nozzle (625, 725) and an open position where the end of the needle is distant from the application orifice; - means for maneuvering the needle in translation between these two positions; - automation means for sequencing the action of the pressure means and the movement of the needle between the open and closed positions; - a) during a positioning step, placing the nozzle (625, 725) so as to fit on top of the rivet head, the application assembly being filled with mastic, the needle being in the closed position, moving the pressure means (215, 415) so as to achieve a predetermined pressure in the feed pipe and the pre-filling chamber of the application assembly; - b) during a coating-beginning step, moving the needle into the open position so as to open the application orifice and to allow flow of the mastic in the cavity and onto the rivet head; - c) during a coating-ending step moving the needle into the closed position and stopping the flow of the mastic; - d) during a movement step, the needle remaining in the closed position, releasing the nozzle (625, 725) from the rivet head and moving the device to the following rivet head, and then resuming the cycle at step a) on said following rivet head;