® NEWTECHNOLOGY FORCONSERVATION ® ® METALSTITCHINGAT DONCASTER'S CORN EXCHANGE This case study describes the repairs carried out by Casting Repairs Ltd of Chesteifield, a company whice specialises in cold metal stitching, a technique which has many advantages in the sympathetic restoration of cast-ironwork. Doncaster's imposing Victorian Com Exchange (Grade II), in the heart of the town, is now in the final stages of a major restoration programme which will rectify the extensive structural damage to its roof and interior following a devastating fire two years ago. Built in the 1870s, the Com Exchange has an elaborate roof design which bears testimony to the skill of the Victorian engineers and the pride taken in creating decorative cast ironwork.The main roof structure consists ofwrought iron curved beams with a span of 18 m which are supported on either side by cast iron columns. Above this is a lantern support feature incorporating decorative cast ironwork. There are also gallery areas running along the length of the building with many fine examples of cast iron decorations including scenes from farming lifeincluding shire horses, plough shears and lambs. The repair project involved structural and decorative ironwork which had become cracked and distorted as the blaze swept through the building reducing its interior a blackened shell. In the aftermath of the fire, architects at Doncaster Metropolitan Borough Council were faced with the problem of restoring its structural integrity without changing its character. Owen Evans,group architect with the Borough Council, felt that the crucial factors were that the repairs should be entirely in keeping with the character of the building and that as much of the original fabric as possible should be preserved. Before repair work could begin, Casting Repairs was required to undertake a complete inspection of the building to establish exactly where the damage had occurred and the most appropriate way of repairing it. This was a mammoth task in itself owing to the numerous cracks and areas of distortion in the structural ironwork. Heat had loosened many of the decorative sections, and shattered many of the castings, leaving numerous CONTEXT49 fragments which had to be pieced together. The inspection revealed that the main roof beams were also severely cracked and distorted. It also became apparent that in certain areas new wrought iron bracings would be required to strengthen the roof as a whole. Although conventional welding methods can be used on the wrought iron beams, a different approach was needed for tl1e more delicate types of decorative cast ironwork. Casting Repairs took the view that cold metal stitching was the only practical way of repairing these. While it is possible to repair cast iron bywelding, this would have involved dismantling hundreds of sections and removing them from the site. With welding there was also the risk of causing further damage by distorting or embrittling the metal. Welding cast iron is a complicated and time consuming operation because the damaged sections have to undergo special heat treatment processes before and after welding in order to achieve a full-strength joint. The cold-metal stitching technique eliminated all of these problems, enabling the work to be carried out in-situwith the minimum of disturbance to the structure of the building. Although the majority of decorative castings were saved through metal stitching, some were simply beyond repair. In cases where decorative castings were cracked into too many fragments to be repaired, identical sections were recast. As the project moved forward, magnetic particle inspection techniques were used to test the integrity of the welds on the main structural members before all of the ironwork was painted to provide corrosion protection. The Com Exchange project is the largest of its kind to be undertaken by Casting Repairs. Apart from the scale and complexity of tl1e work, it has been necessary to avoid disruption to the stallholders in the outdoor market and traders in the connecting Market Hall. Casting Repairs Ltd has been proving the value of this method of repair for more than 40 years and is among an extremely small number of British companies with the necessary expertise. Therefore, each new project is approached with a background of practical knowledge and an awareness of the most effective techniques for completing the repalr. Cold-metal stitching involves drilling holes at right angles to the fracture and then converting them into a slot. Preformed locks are then fitted into the slots to create bridging sections across the fracture and finally holes are drilled along the line of the crack and filled with special screws. The technique results in a repair which is as strong asor even stronger than the original casting. The method can be used on any iron or steel casting of 8 in thickness or greater. A major advantage is that the process can be carried out without the need for the application of heat which removes the risk of distortion and misalignn1ent. Repairs can be carried out in-situ, if necessary, so there is no need for dismantling and reassembly which can be expensive and time consuming on larger projects. Where smaller architectural items are concerned, however, it is often more convenient to take the casting to a workshop. With architectural castings of important historical value, cold-metal stitching often provides the only solution to preserving their unique qualities. More information can be obtained from T Salisbury, Casting Repairs Ltd, Marine House, Hipper Street South, Chesterfield S40 JSS. Tel: 01246 277656 17
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