Lead casting, sheet work and plumbing

Lead is the softest, densest metal used in building, and one of the most durable and malleable. Lead melts at a low temperature and is extracted from the ore ‘galena’.

The eighteenth and nineteenth centuries were the great age of British lead mining and most of the mines in the United Kingdom were located in Wales, Cumberland, Derbyshire and Cornwall. Lead was cast, both to produce architectural decoration, and to produce lead sheet on an open sand casting table.

Lead roofing was popular during the Regency, in part, because it allowed low profile roofs, to be hidden behind the ‘fashionable’ parapet. In the building of Regency homes, lead sheet was also used for guttering, pipes, flashing and solder. Hopper heads, rainwater sumps and urns were made from cast lead. A sad consequence of lead’s widespread use was that many lead workers lived short lives due to the highly toxic nature of lead fumes and powders.

Cast lead

Lead can be moulded in green sand casts, to produce simple items such as sash weights and ornate products like rainwater hoppers and statues. Alternatively, thin workable sheets were used in roof work to make gutters, flashings, soakers and covers for the top of exterior detail such as cornicing. Lead could also be used in other forms. Carbonates, known as white lead, were used by 'colourmen' to add body to oil paints, while oxides were employed in powder form to provide a sheen to patent mastics. Because of these varied characteristics lead has been in use for at least 7,000 years.

Lead sheet can be made in three ways. The sand cast method, where a level bed of sand was prepared on a casting table and molten lead poured out and levelled off with a striking bar. The milled lead method, now some 200 years old, where a block of lead is rolled back and forth through a mill until the required thickness is achieved, and the direct method, where the sheet is made by emersing a watercooled drum in a bath of molten lead and peeling solidified metal from its surface.

Sheet work

Each of these methods provided the means to produce sheets of lead in differing thickness, and thus, weight per square foot, traditionally used for specification purposes.Thin sheet such as 3lb per square foot (3lb lead) being used for items such as flashings and 8lb lead being used for items such as gutters. Today this old system of specifying lead is continued in an analogous system that refers to leads as Code 3, 4, 5 etc. 

Above: Lead bossing.

The thickness of lead sheet, determines the maximum area that it can be laid across, with thinner sheets covering less area. This must be accounted for when repairing or designing leadwork and the appropriate Code  used for each purpose. Because the maximum size to which even a thick lead sheet can be laid as single piece is limited to approximately 2m by 1m, it is usual to fit the material as a series of bays or panels, jointed so as to prevent water from penetrating. This is achieved through the use of ‘rolls’, ‘welts’ and ‘drips’, joints which, importantly, allow the individual sheets to move with changes in temperature.

In skilful hands, lead sheet can be readily manipulated with hand tools without risk of fracture. By the technique of bossing - beating the lead with shaped sticks - it can be worked into the most elaborate shapes. Lead sheet can last upwards of 150 years and requires little maintenance, making it an ideal material and one that should be reinstated to historic buildings during repair works. Old lead fittings can be recycled as feedstock for new sheet.

Plumbing

Lead pipes were used in Regency houses to carry water to the kitchen and newly invented water closet, and to make rainwater down-pipe and soil systems. Pipe could be made in two ways. Either formed from thin sheet wrapped around a rod or ‘mandral’ and seamed by 'bossing' with a shaped hardwood former, or by squeezing molten lead over the mandral. This process of extrusion produced pipe and tube economically. Lead pipe was supported at regular intervals along its length with iron brackets, now often found buried in the corner of the staircase and deep in the wall plaster.

If you are interested in further reading on this topic, these links will provide you with more information:

Norman and Underwood; Sand cast lead

MK Technology's history of metal casting

Historical production and uses of lead

Building Conservation; Underside condensation and corrosion of lead sheet roofs

'The History of the Word Plumber' by James McGill

'Plumbing History' by Agnes Celina