Durability and resistance to decay are two important characteristics necessary for timber used in external cladding and joinery. Heat treatment of wood has a positive effect upon timber decay and Thermowood can achieve resistance class I-II. The timber is drier than that used for general joinery and is more resistant to surface shaking due to the action of UV light. All of these factors contribute to longer surface life than untreated joinery timber, but to ensure protection from the “greying” caused by exposure to the elements, pigmented surface coatings are necessary.