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| EDILIZIA & INTERIOR DESIGN | |||
| Traditional building materials in architectural design - Lecce Stone. In our construction industry, the use of materials with local character indicating a given cultural and geographical area is increasingly widespread and possibly represents a new trend. For example in building materials and interior design, certain kinds of Lecce stone (locally known as Leccisu) are becoming more popular because of their mechanical, functional & aesthetic characteristics. They are also being used for urban facilities. The concept of traditional sources of supply is meaningful in local construction because products can result from systems, methods and procedures inherited from the working methods of previous generations. Nowadays locally popular stones are becoming more frequently used elsewhere although knowledge of their traditional origin is not very widespread. This is one of the reasons why we set up the CONSORZIO PIETRE & DINTORNI, which is intended to promote knowledge and use of this kind of stone and its natural aggregates. Lecce stone is typical of Apulia but still almost unknown in other regions – by contrast with some well-known kinds of southern marble used elsewhere in building structures and ornamental design –and there is a rising interest in our particular stone among architects, engineers and interior designers: this is also the result of innovatory production methods which have increased the range of possible uses. In fact Lecce stone has for centuries been quarried and worked locally, being known in the building trade as a particularly versatile kind of material that is just as easy to work as wood. In technical terms Lecce stone - quarried almost everywhere in the Salento region - is a limestone rock of the Miocene geological era & hence characterised by the presence of numerous fossil fragments, mainly plancton species which are sometimes in a state of almost perfect preservation. On the basis of petrographic examination the main constituent element is calcium carbonate (CaCO3) in the form of calcareous granules (microfossils and fragments of marine fauna fossils dating back about 6 million years) and of limestone cement. The presence of granules of glauconite, quartz, feldspar, muscovite, phosphates and clayey materials, has enriched its overall content and encouraged recognition of the hardness and resistance of Lecce stone over many years, while some kinds can be soft and ductile as well. There are various types of Lecce stone, characterised by differences in colour (varying from white to sandy and honey-like shades), particle sizes, structural uniformity, degree of compactness and geological age. Given these characteristics Lecce stone is known for its wide versatility of uses. Its very ductility resulted in the sculpturing of the many finely decorated friezes, scrolls, capitals and mouldings for which Lecce baroque architecture is well known. As regards its capabilities obviously an architect’s choice of stone is based not only on criteria of cost, function and appropriateness in a given context, but on the equally significant considerations of taste, design style and sensory perception. Nowadays any work done on the surface of Lecce stone results in a search for sensory characteristics: whether it is pleasing to touch or see and the presence of any ‘emotional suggestions’, in a manner of speaking, and Lecce stone does in fact offer ‘suggestions’ of this kind. Of course its geological data determine its technical performance which, rather than being reduced by any kind of processing, is actually enhanced nowadays: for example there have been great improvements in resistance to atmospheric agents and humidity absorption. As well as the excellent technical and aesthetic results of new working methods, it enjoys very effective protection (against staining and water penetration) which means Lecce stone has become very suitable for inside facilities, including floors and walls, bathrooms. Its exceptional intrinsic qualities also make it suitable for the most advanced projects in interior design. In addition some recent research and development work has proved the feasibility of using Lecce stone for structural uses in contemporary architectural design: New processing methods The quality of products is also the result of improved techniques (using numerical control machines, for example) and a description follows of some current methods: Wire Saw Cutting: this expression indicates the surface of slabs obtained by ‘sawing’ on which are visible the traces of disc and blade cutting, while these slabs are generally speaking the object of subsequent decorative work. Smoothing: to attenuate and lighten the stone’s colour while giving it a smooth surface. The slab is used for inside surfaces above all when the latter are subject to intense traffic, such as would soon cause the material’s bright shine to be lost. Bush-hammering: it is one of the oldest methods in use, intended to improve the texture of the stone and give it a rustic, sculptured and relief appearance. This method is also followed to produce different kinds of incisions, in large or fine grains with a wide range of medium finishes. The final surface acquires anti-slip characteristics through which, after bush-hammering, the materials are then suitable for use as outdoor pavements. Antique look: this is a very popular kind of rustic finish which reproduces a particular appearance. Its irregular edges and surfaces remind one of the passing of time, wearing-out caused by frequent use, an illusion of hand-worked material, rather than a natural condition as such. The antique look is obtained by using sifters, machines that use slightly abrasive water blends to ‘wear down’ such pieces of material by rolling, impacting or similar mechanical movements. The residual waste from pieces placed in movement contribute to the system of artificial wearing-down. Grooving: this is best appreciated in a low-angled light, a series of grooves placed laterally are created by using diamond-drill discs or a wide range of variable profile tools. Grooving is mostly used for outdoor pavements because it is particularly suitable for materials with uniform tonality and a fine grain. NATURAL AGGREGATES As well as Lecce stone itself the CONSORZIO PIETRE & DINTORNI is also promoting the use for building purposes of local limestone aggregates, sand and grit, which originate in the same quarries located throughout the Salento area and have the same chemistry and morphology as the stone itself. The term aggregates used to define these sands and grits is however inappropriate because their role is not at all passive or secondary and natural aggregates have an important function in the make-up of mortar, whatever kind of binder is used. In fact natural aggregates are a blend of substances sourced from the land and their chemical and physical composition can vary considerably, although quarried only a short distance away. As regards volumes and characteristics these aggregates have a very significant function in the production of cement-based mortars. Whether they are defined as ‘sands’ or ‘grits’ is a matter of the size (in any case less than 4-5 mm) of the granules making up an aggregate. Nowadays there is automatic batching of components like sands or grits, cement, ferrous oxide and water-repellent and anti-mould elements, moreover the constant and systematic checks made on materials and mortars, serve to ensure high standards of quality in building products. One should add it is also the care taken in production processes, just as in working natural stone itself, which ensures that the quarried material becomes an aesthetically pleasant object. The Italian regulation on production of stone materials is UNI 8458. |
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