Abstract: A device for treating the surfaces of structures and ships, even under water, with a spray medium which cleans, preserves, or coats, and is sprayed onto the surface which is to be treated by way of a pressurized gas flow via an at least partially flexible conduit which leads to the work location and is provided with an outlet nozzle. The outlet nozzle, which is constructed as a Laval nozzle, is provided with a funnel-shaped nozzle adapter which has a longitudinally extending, parabolic inner chamber. A controllable shunt, capable of bypassing the spray medium source may be provided for the pressurized gas between the pressurized gas source and the line leading to the outlet nozzle so that the device can be used under water.