A dispenser tool (42) is provided with multiple cartridges for dispensing viscous material onto the surface (5′) of a wind turbine blade (5). The dispenser tool (42) is advantageously part of a robot system used to work the surface (5′) of the blade (5). The system is configured for bringing the nozzle of a selected cartridge into the vicinity of the surface (5′) and orienting the dispenser tool (42) relatively to the surface (5′) such that the nozzle (46) of the corresponding selected cartridge (44) is at the surface (5′) for providing viscous material onto the surface (5′) from the selected cartridge (44) while moving the nozzle (46) along the surface (5′).