Candidate materials for weld overlay coating of waterwalls have been investigated to determine corrosion rates and investigate corrosion mechanisms. Test waterwall panels with single layer weld overlays were exposed for a total of 7727 h in a 75 MW.tot circulating fluidised bed boiler with 470°C/65 bar steam data. The fuel was 60% industrial waste and 40% household waste, resulting in very corrosive conditions. Six weld overlay materials were tested: the well proven alloy 625, a modified alloy 625 in which niobium was replaced by tungsten, alloy 59, alloy 22, a cheaper nickel base alloy 650 which contains some iron and a 310 grade stainless steel. Significant material loss occurred for all the panels. The nickel base alloys mainly developed hemispherical pits while the stainless steel exhibited relatively uniform corrosion. This means that the progress of the corrosion process is easier to monitor by inspection for the stainless steel. Detailed analyses of the corrosion products showed that conditions were sufficiently oxidising to allow formation of metal oxides, but that there were also extensive deposits of alkali and heavy metal chlorides. The corrosion mechanism is discussed in terms of formation of a molten salt layer which dissolves the oxide layer by fluxing. © 2009 Institute of Materials, Minerals and Mining.