Abstract: A method and apparatus for cleaning the interior surfaces of buildings, especially the ceilings of office buildings, involves producing a fine mist of cleaning liquid which is sprayed onto said surfaces. This fine mist is produced by pumping a cleaning liquid from a container by means of a pump which leads to a delivery tube and which produces a pressure of at least 300 psi, the liquid being atomized by a nozzle having a breadth less than 0.020 inches. The amount of liquid passing through the pump is more than 5 times the amount passing through the nozzle, and the remainder of this liquid is returned by a bypass line to the container.