The principal use of lead today is in flashings and roof coverings, and it is easy to overlook the extraordinary versatility of this dull-grey material. Not only is lead also used for those small H-section strips known as cames for fixing the glass quarries together in stained glass windows and leaded lights, but its impermeability, low melting point and soft malleable nature makes lead ideal for sculptural decoration and ornamentation. Cast lead ornament can be found in many churches and chapels throughout the country, including the decoration of rainwater pipes and hoppers, finials and even fonts, as well as forming the decorative cladding for domes and spires from the Middle Ages to the present day.
Lead has been known to last hundreds of years even in exposed conditions. This is because the surface of rain-washed lead carbonates to form a protective layer which prevents deterioration. When correctly installed, the greatest threat to all forms of leadwork is not so much weathering as the ease with which the material can be melted down and reused. It seems likely that many medieval cast lead fonts, for example, were melted down to make bullets in the 17th century in particular. Theft remains common, and ignorance of the value of original medieval craftsmanship has also taken its toll in countless restorations.
A BRIEF HISTORY
The first architectural use of leadwork in this country was probably by the Romans who recognised its advantages as a conduit for water in particular, and the first known use of the material on a church roof was as early as AD650 at Lindisfarne where it replaced Scottish thatch. The use of lead sheet in the Norman period is better documented and included weatherings to protect exposed stonework.
Sand cast lead sheets have been used extensively as a roof covering since the Norman period, and although most early and vernacular architecture relied on broad eaves, the use of parapets led to the introduction of parapet gutters and gargoyles to throw the water clear. The rainwater pipe was a natural development. One of the first instances of its use is identified in a letter quoted by Lawrence Weaver in his book English Leadwork. Accordingly, King Henry III wrote to the Keeper of the Works at the Tower of London in the year 1241 as follows: 'We command you to cause all the leaden gutters of the great tower through which rainwater should fall from the summit of the same tower to be carried down to the ground, so that the walls of the said tower, which has been newly whitewashed, may be no wise injured by the dropping of rainwater nor be easily weakened'.
Medieval church roofs were sometimes elaborately ornamented with finials including figures of saints, and spires were frequently clad in lead, such as the magnificent twisted spire at Chesterfield. Cast rainwater pipes remained rare as most churches continued to use gargoyles, but there are examples as at Kettering, Northamptonshire (15th century).
By the late 15th century lead was growing more expensive as the more accessible sources of lead ore were being exhausted and deeper seams had to be found. Then, in 1539, the Dissolution of the monasteries provided large quantities of recycled lead and gave fresh impetus to the development of leadwork. Elaborate ornamentation began to appear more frequently on lead rainwater hoppers and cisterns, usually incorporating dates and heraldic motifs, particularly on secular houses. Other artefacts included statues and urns, candelabra and coats of arms.
Early leadwork was all sand cast. Sheets were made by pouring molten metal over a bed of moist sand which had been smoothed meticulously. The thickness was made as even as possible by drawing a board or strickle across the surface, supported at either side by rails set at the height required.
As today, the principal use of these sand cast lead sheets was in cladding roofs and as weatherings, but they could also be used in a decorative capacity by dressing the metal to an ornamental shape, usually over a timber or metal core to ensure that the object retained its form. Hammering the surface produced a fine grain structural texture which was less likely to corrode. By soldering the sheet afterwards, a weather-tight seal could be achieved, making it ideal for external uses such as the cladding of finials, provided the fit was sufficiently loose to allow for expansion and contraction.
Surface decoration was applied in a number of different ways. Raised decoration could be applied by bossing (beating) the lead sheet into a die or by fixing cast embellishments to it. The surface of the sheet could also be painted or gilded, and tin foil was sometimes applied to the heated surface with a resin flux so that the two metals partially fused to produce a harder shiny surface.
Where lead is to be painted today, the best results can be achieved using a two-part etching primer. Conventional paints do not adhere well to the surface of the metal, and as they crack and flake they trap moisture which causes the underlying lead to corrode.
Decorative leadwork was also produced by casting the lead in sand moulds which had been impressed with a carved wooden former. To make the font (illustrated at the top of the page) for example, it seems likely that only three patterns were used, as the scroll motif and the two different seated figures are repeated in an arcaded design around the tub-like form. This font was probably cast in sections using a flat bed of sand with the decoration pressed into it. Once cast, the sections were probably reheated and bent into a curved form before being soldered together.
Permanent chill moulds were introduced much later, probably following the industrial revolution. They are called chill moulds because they are made of metal, which causes the lead to solidify on contact with the cool surface. Today they are usually made of cast aluminium, but cast iron and a variety of other metals were commonly used in the past. Moulds are usually in two or more parts enclosing the entire object, and the parts are disassembled to release the finished casting. Finishing must be carried out carefully to avoid creating any toxic dust.
To make a chill mould the component to be cast is first made in lead in the conventional manner using sand castings soldered together as necessary. From this original, a foundry then makes plaster moulds, then a new plaster model and finally the cast iron mould.
THE DEMISE OF SAND CAST LEAD
Sand cast lead sheets are still produced in relatively small quantities in the UK for conservation work. However, at the turn of the century milled or rolled lead sheet production began to take over from sand casting and rapidly emerged as the principal method of producing lead sheet. In this method of production, which dates from the mid 18th century, lead is cast in a slab of about 125 mm thick, weighing two tonnes or more. When cooled, the slab is rolled out into sheets by passing it through heavy rollers repeatedly, to produce a progressively thinner sheet. When the required thickness is achieved, the sheet is slit into widths and cut to length.
Although milled lead is the only material covered by a British Standard and its thickness is more accurately controlled, the Lead Development Association considers that there is little difference in performance between well made sand cast and milled lead sheet. The principal difference lies in the less regular appearance of sand cast lead. The minimum thickness of sand cast lead sheets is approximately code 7 (seven pounds per square foot), while milled lead sheet is available in codes 3 to 8.
It was the introduction of cast iron which finally heralded the demise of lead rainwater systems. In the 19th century cast iron systems generally copied the design of leadwork, but with modifications. In particular, the much stronger nature of the material enabled the use of shallow collars and two point fixings. Unfortunately, in the various stylistic revivals of the Victorian period, new leadwork tended to copy ironwork details. Evidence of this can also be seen at the Tower of London where, as you exit The Bloody Tower by the external staircase, you can see how a rainwater shoe has distorted because the shallow collar cannot support the lower section. The date on the work is 1974.
LEAD RAINWATER SYSTEMS
The Tower of London is an excellent place to study the history of rainwater discharge systems. They mostly consist of cast iron or lead.
In 1992, 750 years after King Henrys letter, Terry Fillary and his son Paul were summoned to the Tower by Martin Caroe, of Caroe & Partners, to discuss the installation of new cast lead rainwater pipes on the wall walks and on the Wakefield and Lanthorn Towers. Over the years many of the lead pipes had been replaced with cast iron pipes, many of which in turn now needed replacement. It was decided to use lead for the replacements.
The new pipes and collars were made in the style of the existing pipes on the north elevation of the Bloody Tower. The 114mm square pipes were formed from code ten sand cast sheet, two metres in length. The collars and ears were cast in aluminium chill molds. The fixings for each pipe were two stainless steel ear plates and four stainless steel coach bolts. Although the collars were required to be plain and not ornamental, Terry Fillary confesses to having cast a crown and QEII 1993 on the collars of the last smaller pipes, which can be seen on the right hand side of the road by the Traitors Gate.
In principle, the same materials and details should always be used on historic buildings as the existing, unless the restoration of earlier details can be justified. Where lead is concerned, the temptation is to use less expensive substitutes. However, the life expectancy of lead is in excess of 200 years, and as the material will not rust, painting is not necessary. As a result, on high and large buildings such as churches, the cost savings of using lead can be colossal in the long run. The use of alternative materials may be justified where there is an over-riding need to reduce the risk of theft, where the lead is highly accessible and where, in remote buildings, there is little chance of theft being spotted.
Because of the weight of lead, rainwater pipes are best installed using the new small type of rope block and tackle used on sailing boats: a 3x4 pulley that can pass through the pipe is required. First get a safe fixing above the outlet from the roof; attach the lifting tackle and pull the hopper up into place, fixing with stainless steel coach bolts. Then pass the lifting tackle down though the hopper head and the first pipe, with the spigot of the hopper in the pipe socket, down to the ground. Attach the hock to a stout piece of timber across the lower end of the pipe and pull it up into place. This lifting method will not damage or scuff the surface appearance of the pipe. When the second pipe is in place only half the effective pipe collar should be used, so each pipe is totally independent of the next one. This is to allow for thermal movement and creep. Each joint is left open so that if the pipe blocks it will not be too long before it is detected.
The action of the weather on lead, alternating between wet and dry, creates a very hard insoluble surface patina. This hard coating, left undisturbed, will protect the lead from corrosion and therefore prevent damage to the environment. On new works an application of patination oil will prevent corrosion initially while the patina is being established.
In rainwater pipes a good air flow is necessary to create the wetting and drying process required to provide the conditions for a protective patina to be formed. Direct connection to the drainage system should be avoided, as this will cause condensation within the pipe with resultant leaching of the lead when it rains, in much the same manner as the underside lead corrosion of lead sheet roofs.
To maintain a good airflow, a rainwater shoe approximately 150mm above the trapped gully should be specified. This method is preferred for another reason - if the underground drainage system becomes blocked, water will spill over the gully, thus giving a visual warning that there is a problem. With direct connection to the drain however, water would build up within the pipe work, escaping from the collar joints above, running down the walls, often undetected, causing much long term damage to the fabric of the building.
At the top of the rainwater system, a hopper head should be used not a direct connection to the discharge from the roof, for exactly the same reasons as described for the base of the stack.
Drive or pipe nails should not be used when fixing rainwater pipes as they damage the fabric of the building. The rule of conservation should be 'dont use a hammer when a spanner will do'. Work must be reversible, and removable without damage.
This article is reproduced from The Conservation and Repair of Ecclesiastical Buildings, 1999
TERRY FILLARY works part-time teaching leadwork at college and sometimes trains interested people in his workshop. He also lectures on leadwork and is currently writing a book on the subject.
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