Copper as a dpc should be annealed, at least 0.25 mm thick and have a nominal weight of 2.28 kg/m2. Copper is an effective barrier to moisture and water, it is flexible, has high tensile strength and can suffer distortion due to moderate settlement in a wall without damage. It is an expensive material and is little used today as a dpc above ground. When used as a dpc, it may cause staining of wall surfaces due to the oxide that forms. It is spread on an even bed of mortar and lapped at least 100 mm or the width of the dpc at running joints and intersections.