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Throughout history, slate has been one of the most commonly used roofing materials in Europe. Yet surprisingly little is known about its composition and properties compared to other building materials like granite and marble.
The EU-funded TOMOSLATE project helped to fill major knowledge gaps surrounding this natural building stone. As a result, the researchers were able to propose solutions to some of the key problems facing the European roofing slate industry.
“The project addressed the need for a proper scientific background for roofing slate,” says Víctor Cárdenes, the principal researcher who was funded through the EU Marie Skłodowska-Curie Actions programme.
At the University of Ghent in Belgium, the project team applied X-ray micro-computed tomography (MCT) and other state-of-the-art techniques to study the characteristics of roofing slates.
“The key results of the project were a method to prevent weathering on roofing slates, which is currently under industrial development; a scientific classification for roofing slates, aimed to provide the sector with standard procedures; and several scientific publications,” says Cárdenes.
Spray painting protection
The project team studied the mechanical behaviour of slates during free-thaw cycles and the evolution of mineral changes during weathering.
A key mechanism caused by weathering is iron sulphides oxidation. To counteract this, the project developed a protective paint coating that is sprayed on to roofing slates. A company in Barcelona produced prototypes of the paint which are being tested in the field at the Slate Technological Centre in Galicia, Spain.
The MCT technique revealed in great detail the occurrence of iron sulphides on slate, enabling a prediction to be made about the oxidation risk of any given roofing slates. An unexpected result was the opening up of a new line of research relating to the geological aspects of iron sulphides, with potential applications in ore mining and in the study of the origins of rocks (petrology).
Getting to know roofing slates
Previously, a lack of a standard classification for different types of roofing slate led to confusion about their characteristics. Thus, it was not obvious which types would prove the most durable and weatherproof in particular environments. The new knowledge was used to propose a concise and scientific classification, based on petrology and colour.
The project team defined four rock types used as roofing slates. Although part of a continuous sequence, this classification distinguishes different constructive properties, especially mechanical behaviour. Colour results from the rock’s mineralogy. Roofing slates fall into three colour families – purple-red, green and black. Thus, the project defined a total of 12 roofing-slate types with characteristic mechanical and weathering behaviours. Cárdenes believes this is the world’s first such scientific classification of roofing slates.
The anti-weathering paint and the classification system will also help preserve Europe’s architectural heritage, for example, by enabling damaged roofing tiles to be replaced by those with characteristics most appropriate for the climatic conditions.
To disseminate their findings, the project team gave talks to quarry operators, the roofing and slate industries, builders, architects and visitors to thematic museums, all of whom gained a better understanding of the nature of roofing slates.
“We now have greater awareness of a very important natural stone that’s used abundantly in Europe and the rest of the world,” concludes Cárdenes. “The information gained in this project will help revitalise the European roofing-slate sector.”