The Bishop of Melbourne ordered a complete town of prefabricated corrugated iron buildings to house the numerous gold-rush immigrants to Australia. The gold field sites were a mass of tents, with no facilities. The prefabricated buildings were a quick and cheap way to provide housing and facilities. The buildings were supplied by Samuel Hemming's Patent Portable House Manufactory in Bristol. The firm erected them at its Clift House works (near today's Riverside Garden Centre) for checking before dismantling them and shipping them to Australia in 1855. Galvanised corrugated iron made in the city was one of Bristol's biggest exports in the later 1800s. Galvanising is a method of rust-proofing iron by coating it with hot zinc. After the 1920s, Bristol had the only zinc smelting plant in England at Avonmouth, processing zinc ore brought from Australia. It closed in 2003.