The corrosion of common fastener materials now in use - mild steel, zinc-coated steel, aluminium and Sanbond Z-coated steel – has been evaluated after nine years’ exposure outdoors in untreated and heat-treated (thermally modified) spruce (Picea abies). Spruce from south-western Sweden was used. The heat-treatment was carried out in Finland by Stora-Enso Oy according to the ThermoWood process at a maximum temperature of 220 °C for five hours. The results so far confirm the findings after two years’ exposure that the corrosion of fasteners in heat-treated wood according to the particular specification is more severe than in untreated wood. Mild steel and zinc-coated steel has been most susceptible. Stainless steel is hardly attacked at all.

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