Abstract: A method for coating a component having: a metallic substrate; a ceramic coating having one or more ceramic coating layers atop the substrate; and a cooling passageway system comprising a plurality of feed passageways extending from one or more inlet ports and a plurality of outlet passageways. The outlet passageways have openings in the coating. The method involves: applying a slurry aluminide to the plurality of outlet passageways; coupling the one or more inlets to a suction source; applying an external gas flow to the component, the suction source drawing the external gas in through the outlet passageways and out through the one or more inlet ports, the external gas flow comprising at least 50% by volume combined one to all of Ar, He, and H2; and while the suction source is drawing the external gas, heating the component to aluminize the cooling passageway system.