Lead is an excellent building material that provides a consistency of performance over many years. It also provides a reliability that is far superior to man-made products.

There are however, three main types of lead that many people may not know about and there are some differences in their performance that need to be considered when specifying and installing lead.

Code of practice and guaranteesLead sheet has always been associated with quality

and durability in the built environment and the

work of the LSA is to advance and maintain that

reputation.

As a result, all technical advice in respect of

application and installation as detailed in the

Rolled Lead Sheet Manual, only relates to use of

rolled lead sheet conforming to BS EN 12588.

For this reason the 25 Year Guarantee Scheme

offered by members of the Lead Contractors

Association is only available when Rolled lead

Sheet to BSEN12588 is used, or traditional sand

cast sheet from an approved manufacturer, a list of

which is available from the LCA.

The main differences between the three types of lead are in the way they are manufactured.

Rolled lead sheet• This is made by passing lead through a rolling mill. Successive ‘passes’ through the mill squeeze the lead to the required consistently smooth finish and thickness. This process is common to all high quality metal manufacturing and has been the most commonly used method of production since the 1920s.

• Rolled lead sheet is the only lead sheet for building and construction manufactured to a British Standard – BS EN 12588. This Standard specifies thickness and chemical composition criteria, ensuring products manufactured to this Standard perform most effectively in resisting creep and thermal fatigue when compared with non-BS products.

• The British Standard also provides guidelines for length and width and stipulates that the sheet is free from inclusions and laminates. For building purposes it is available in Codes 3-8.

• British Standard lead is included within the European Union’s list of Harmonized materials and is eligible to carry the CE mark when the Construction Products Regulations come into force on 1st July 2013.

• The quality of material secured through the British Standard manufacturing process make rolled lead sheet a successful export product.

Lead - the differenttypes explained

The different types of lead

Information Sheet

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Lead - the different types explained

Lead Sheet Association

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E: info@leadsheet.co.uk

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Information Sheet

Machine cast lead or Direct Method• This form of lead is made my immersing a rotating water-cooled metal drum into a bath of molten lead at a constant temperature. As the drum turns, the lead solidifies on the surface and is peeled off as it emerges from the melt, slit to width and wound into coils. Different thicknesses of this type of lead are made by varying the rotation speed of the drum and the depth of immersion. This process of lead manufacture is often referred to as the Direct Method.

• Machine cast lead was first introduced in the UK in the 1980s. It differs from sand cast and rolled lead sheet in both surface finish and grain structure. The surface of the machine cast lead not in contact with the rotating drum has a slightly dimpled finish.

• Mainly due to the potential variation in thickness, machine cast lead does not conform to British Standard. Some manufacturers in the UK do have a British Board of Agrément Certificate, but these only detail the chemical, physical and technical characteristics of an individual manufacturer’s product or processes.

• Research carried out by the University of Cambridge over the last 27 years, comparing both rolled and machine cast lead, has shown that whilst both are very durable materials and have performed well, machine cast lead had started to exhibit early signs of blistering towards the end of this period.

• Machine cast lead is generally sold in Codes 3-8 in the UK and it can emanate from a variety of locations around the world. South America and Eastern Europe are common sources of machine cast material.

Sand cast lead • This form of lead is still made today by the traditional method of pouring molten lead over a bed of prepared sand on a casting bench. A relatively small amount of this lead is produced by specialists, primarily for replacing old cast lead roofing on a like-for-like basis on heritage properties.

• The consistency of thickness and composition of sand cast lead is dependent upon the skill of the caster and the blend of the reprocessed old sheet with new ingots used in its manufacture. Its appearance can also differ from that of rolled and machine cast lead sheet as the side of the sheet cast onto the sand has a smoother finish than that exposed to the atmosphere. The material is normally available in thicker gauges, usually Codes 6-8.

• Sand cast lead has a similar pedigree to rolled lead in terms of its performance on many historic buildings. This is because the sheet is used in greater thicknesses compared to rolled lead sheet in order to compensate for the variations in manufacturing techniques and thickness.

• Sand cast lead is not made to British Standard and does not have a British Board of Agrément Certificate.

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