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Volume supply of quality new and reclaimed slates is a thing of the past. Today there's just not enough natural stone slate to meet demand, and it is generally viewed that what resources there are should be saved for use on buildings of architectural importance.In the 1960s and '70s, it was possible to strip roofs and reclaim slates in substantial numbers from buildings being demolished. That is no longer the case.`The situation is now so bad that many stockists and roofing contractors are unable to price for the supply of major projects,' says Marshalls' roofing product manager, Ian O'Connor. `Instead, they prefer to limit their involvement to small extensions or patching contracts where as few as 200 to 400 used slates are required.'Stringent checking procedures are followed to ensure consistency of quality, colours, grades and thicknesses. Achieving a consistent aesthetic finish to the roof comes at a price, and satisfying the specifier can therefore be difficult, particularly on large roofing projects.Some argue that newly quarried natural slate should always be used. However, increasing shortages of quarried slate and the subsequent costs make them prohibitive in many applications. For instance, developers are often put off acquiring large old buildings because planners insist on natural stone for the roof. These types of properties are sadly left to decay instead of being renovated.In circumstances where the character of the building calls for natural stone slate, natural blue slate is often allowed as an alternative because it is `natural'. Blue slate, which is mainly imported, is thinner and more uniform in colour but lacks the character of the new generation of artificial stone slate.The look of a traditional stone roof can be created at a fraction of the cost, using reproduction roof slates. This approach is providing a popular alternative in `stone sensitive' areas of the UK to ensure buildings remain sympathetic to their surroundings.Advances in production methods have meant that manufacturers have overcome difficulties previously associated with reproduction slates. One such problem, colour leaching, occurred due to the unstable nature of carboniferous- based dyes and the porous nature of the concrete slate. Marshalls has overcome this with its Heritage slates. These retain their colour through use of waterproofers and plasticisers, together with dyes containing a uv-resistant stable oxide base. In addition, the slates weather over time, providing an even more realistic appearance.Reproduction slates cost about a third of the price of natural reclaimed stone slate and one fifth that of new quarried slate. Realistic pricing will play a key role in encouraging the use of these tiles in place of plain concrete alternatives.Fifteen different slate sizes have been created by Marshalls using moulds taken from original slates chosen for their riven faced features to emulate the character of a reducing coursed random sized stone slate roof.Fixing costs are reduced, as the roofing contractor is provided with a computer generated layout showing where each length of slate is to be laid up the pitch of the roof. The need to sort, dress and cut slates is almost eliminated as each individual slate is cross- referenced and linked to a computer generated layout provided with every order.Manufacturers offer a range of colours to match existing slate in stone sensitive regions. For instance, Marshalls Weatherworn is charcoal in colour and replicates blackened roofs found in our towns and cities as a result of the pollution generated in the days of heavy industry. This has proved popular with planners who prefer new developments to blend, rather than contrast with their immediate environment.Another example is Old Yorkstone, which emulates the unique patterns typical of the north of England. The patterning gives a similar effect to slates which have been turned over to produce the fresh side to the elements during renovation. The resultant effect is that of original colouring and a certain amount of weathering which would have affected the slate around the leading edges in their original location.