Historic Church's Copper Roof Good After 213 Years

Abstract

An examination of English-made copper sheets taken from the roof of Christ Church, Philadelphia, Pa. after 213 years' exposure shows a weathering loss of 0.007-inch at thinnest areas, equivalent to a corrosion rate of 0.000033-inch per year. It is believed the essentially rural character of the atmosphere during early exposure of these sheets has contributed to their life. Recent corrosion tests on copper sheets in an industrial atmosphere, show somewhat higher rates. Rockwell hardness of 15T 61 to 63 indicated the sheets on the church had been finished with a slight temper. Screws driven through the center of some sheets twenty years ago restricted expansion and contraction and caused fatigue cracks. Some of the 3-inch wrought iron nails originally used to fasten the copper pans to the roof boards had corroded through at the roof line, possibly as a result of condensation.