- a naturally occurring metal, the first to be smelted by man some 4000 years ago, and long used by the building industry for both practical and aesthetic purposes. Old lead can be an important historic document, there is a long tradition of inscribing into lead. It is malleable and weathers sympathetically, laid properly it can be virtually maintenance free. Laying is a skilled operation, in which factors such as thermal movement and degree of pitch, dictate matters such as size of sheet, thickness of lead, type of joint, and method of fixing (Illustration). Lead is available in codes, which can be selected to suit a particular circumstance. Code 3 means the lead weighs 3lbs per square foot, code 8, weighs 8 lbs per square foot. Labels are colour coded eg green for code 3, red for code 5 etc. While lead seems heavy, as a roofing material its actually lighter than thatch, tiles, slate etc. It is also very good sound insulation. Lead work is a generic term for anything cast in lead, for example, rainwater goods (rainwater heads are frequently highly decorated and dated), cisterns, sundials, vases etc. Lead will however corrode most other metals it comes into contact with through "dissimilar metal contact".
Very early lead can have a high silver content which can be extracted in recycling. This can be a useful bonus when re-roofing early buildings, but attracts thieves.
Bossed - a method of working where the lead is hammered into shape eg to form a corner.
Cast lead sheet - lead sheet made by passing molten lead over a bed of sand. A traditional method of providing sheet, it can vary in thickness but has a textured surface from contact with the sand, it's quite heavy, usually 8-10 lbs per squ ft.
Indorous felt - a fleecy felt which prevents lead sticking to its substrate. (Illustration)
Joints - can be divided into five main types -