Abstract: It is possible to clean high temperature (over 400, e. g. over 1000, degrees F) surfaces in a time and cost efficient manner by using a liquid-cooled ceramic welding lance to direct (at super-atmospheric pressure) a blasting media at the surfaces to be cleaned. The blasting media is preferably combustible at the temperature of the environment surrounding the surfaces, and may include one or more organic agricultural abrasive materials (preferably black walnut shells) as the sole or primary constituent. Blasting may be practiced by directing the media at the surfaces to be cleaned at a pressure of between about 40-100 psi, for example continuously for as long as is necessary (e. g. more than 30 minutes), without any need to remove the lance from the environment. The method is desirably practiced to clean, while in operation or in situ, metal surfaces having scale buildup which adversely affects the ability of the metal surfaces to transfer heat, reheat tubes, process tubes, furnace surfaces, or the like.