The Building Conservation Directory 2020

82 T H E B U I L D I N G CO N S E R VAT I O N D I R E C TO R Y 2 0 2 0 C AT H E D R A L COMMU N I C AT I ON S the casting process and a weak point in future. Any solder patches or soldered joints on pipes are therefore cut out and set aside for further reuse. The lead sheet is then loaded into gas- fired pots for melting down. The melting point of lead is 327°C (621°F). When the lead reaches melting point any impurities which are ingrained in the lead float to the surface and are skimmed off and collected, and this waste material can then be sold separately to another company for refinement, so nothing is wasted. Once the molten lead has been skimmed, it is cast into ingots. This is done by hand ladling the molten lead from the pot into ingot moulds, with each ingot weighing approximately 40kg. These are then taken to the casting area, ready for the next step in the process. In essence, producing sand cast lead consists of throwing molten lead down a bed of prepared damp sand. This method has changed little since Roman times and the equipment needed is very basic. A predetermined amount of sand is watered and thoroughly mixed using wooden paddles, it is then roughly spread across the casting table. The sand is then roughly levelled off with a bar of wood called a strickle or strike which is propelled by two men at each end and supported by the side beams of the table. The strickle/strike is then used to ram the sand to make it solid again, before being drawn across the table again to level it off at the required level. The surface of the sand is then ready for smoothing to the required finish using hand- held copper planes. While the sand is being prepared for the casting, the lead in the melting pot has been brought up to the required temperature. This is then ladled into a trough at the top end of the casting table. When sufficient lead has been transferred, the trough is lifted by means of a pulley wheel and handle, and the molten lead is poured down the surface of the table. While the lead remains molten, and again using the same strickle/strike, the lead is planed off to give its required thickness. This is determined by a number of factors, namely the speed at which the lead is thrown down the table, the heat of the metal and the speed with which it is planed off, but it also has a lot to do with the experience of the craftspeople involved in the casting. The excess lead is collected in the tail pan and is then transferred back into the pot at the head of the table for recycling. As soon as the men with the strickle/ strike reach the bottom of the table, the lead behind them has already set and can be marked and cut virtually immediately. All the lead used from the casting is measured for each specific job and is cut to size, rolled and weighed individually. Any lead then left on the table is cut up and again recycled. In addition to being used on roofs, cast lead is also used for rainwater goods, heads and downpipes. If these are required with mouldings and patterns, a timber pattern is used to press into the sand on the table before the molten lead is thrown. These are then cut out and formed by hand into the pipes and heads as required. The result of this process is that cast lead is often less uniform than milled lead, its quality depending entirely on the craftsmanship of the person who casts it. Today, however, there are skilled craftspeople spread across the country producing cast lead which complies with the recommendations and proposals of the British Standard Institute codes, and quality is strictly controlled, typically to ISO 9001 quality management standard. The thicknesses of their produce can easily meet the code’s recommendations of plus or minus five per cent, which assures architects and specifiers that they can recommend this material with confidence. To ensure quality specifications will often state that the lead must be from a manufacturer with the appropriate BBA Agrément certification and that it meets the relevant British Standard and the criteria set by the relevant code. If a cast lead roof is also laid to good standards by a fully trained craftsperson, the normal life expectancy for this remarkable roofing material is at least 200 years. Sand cast lead is without question the ultimate choice when specifying the finest covering for historic buildings of significance that requires a long and service free cover. JONATHAN CASTLEMAN DSc (Hons) is by trade a time-served lead plumber and received an Honorary Doctorate in Science from Leicester University in 2010 in recognition of his work in the restoration and conservation sector. Jon made the lead inner casket for the remains of King Richard III, found buried under a car park – the site of a former chapel – in Leicester in 2012. He was also tasked with welding it shut. Two photos taken in the 1950s showing (left) the sand bed being carefully finished with hand-held copper planes ready for casting (right) (Photos: Jonathan Castleman) The same process today; apart from the dust masks and protective overalls, little has changed. (Photo: Norman & Underwood)