Abstract: Coating with clinging foam the upper interior walls of a generally horizontal pipe. A high-pressure pump delivers jetting water to a nozzle through a normally reeled hose. The nozzle has a body divided by a pressure-actuated valve into two chambers, the first one having a series of high-pressure jet exits. The valve is normally open and, when the high pressure is off, leads into a second chamber having a foam outlet. Two pump and metering devices and a compressor then deliver water, chemical and air mixed into a damp sloppy foam to the hose and thence to the nozzle. A skid supports the nozzle and has a series of skid rods regularly spaced around it. A gravity-operated device at the outlet is connected to the foam outlet from the nozzle's second chamber and causes expulsion of the foam toward the walls of said pipe lying along a predetermined upper sector only.