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Lead

- List of lead illustrations

- 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.

Glossary
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 -

  1. Drip, formed where lead is lapped over a step in the substrate.
  2. Hollow roll, is formed when two sheets meet to form a standing seam which is turned into a roll. (Illustration 1), (Illustration 2)
  3. Lap, where one sheet is simply lapped over the other.
  4. Welt, formed by turning the undercloak up by approx one inch, and the overcloak by two inches, which is then folded over and lightly pressed flat.
  5. Wood roll, formed by dressing the edges of adjoining sheets over a wood core (Illustration).
Lead burned - lead which is welded.
Milled lead sheet - manufactured by passing lead through heavy rolling mills.
Overcloak - the overlapping edge of a lead sheet.
Patination oil - used to prevent the white carbonate which is produced by new lead (Illustration), until a patina is formed.
Primary lead - lead which has been mined.
Secondary lead - lead which has been recycled.
Substrate - the material on which the lead is laid. (Lead deteriorates markedly on its underside from condensation, so the composition of the substrate is very important)
Undercloak - the upper edge of the sheet which is covered by the overcloak.