System for applying an inorganic coating material to a surface comprising: - a spray nozzle unit, comprising the following features: - a first end portion with a first connection for a first supply hose, for supplying a first component of the coating material, - a second end portion for discharging the coating material from the spray nozzle unit, - a connection unit for mixing and transporting components of the coating material from the first end portion to the second end portion, - wherein the connection unit comprises a mixing chamber with at least one further connection (21, 31) for supplying a second component of the coating material, - and wherein at least one electronic sensor is mounted on the connection unit to detect an oscillation amplitude arising at the connection unit, - a data processing unit for acquiring the oscillation amplitude detected by the electronic sensor of the spray nozzle unit and for calculating an actual frequency spectrum or target frequency spectrum from the oscillation amplitudes detected, - a comparison unit for comparing an actual frequency spectrum with a target frequency spectrum and generating control data, - a control unit, wherein the control unit - generates a warning signal when the control data lie outside a defined range, and/or - varies the volume flow of at least one of the components of the coating material depending on the control data generated by the comparison unit. - a spray nozzle unit, comprising the following features: - a first end portion with a first connection for a first supply hose, for supplying a first component of the coating material, - a second end portion for discharging the coating material from the spray nozzle unit, - a connection unit for mixing and transporting components of the coating material from the first end portion to the second end portion, - wherein the connection unit comprises a mixing chamber with at least one further connection (21, 31) for supplying a second component of the coating material, - and wherein at least one electronic sensor is mounted on the connection unit to detect an oscillation amplitude arising at the connection unit, - a first end portion with a first connection for a first supply hose, for supplying a first component of the coating material, - a second end portion for discharging the coating material from the spray nozzle unit, - a connection unit for mixing and transporting components of the coating material from the first end portion to the second end portion, - wherein the connection unit comprises a mixing chamber with at least one further connection (21, 31) for supplying a second component of the coating material, - and wherein at least one electronic sensor is mounted on the connection unit to detect an oscillation amplitude arising at the connection unit, - a data processing unit for acquiring the oscillation amplitude detected by the electronic sensor of the spray nozzle unit and for calculating an actual frequency spectrum or target frequency spectrum from the oscillation amplitudes detected, - a comparison unit for comparing an actual frequency spectrum with a target frequency spectrum and generating control data, - a control unit, - generates a warning signal when the control data lie outside a defined range, - varies the volume flow of at least one of the components of the coating material depending on the control data generated by the comparison unit.