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In the Nordic countries, phyllite, mica schist and schistose quartzite have been used in centuries for roofing purposes, and there are examples of quarries that have delivered roofing material since the middle age. The long Nordic traditions evidence for good durability and performance of many of these natural stone varieties, and it is not uncommon that slate roofs last longer than the house itself, and are being re-used.
Slated roofs are still popular. But the situation has changed dramatically the last e.g. fifteen years. World stone production has recorded an increase of over 200 % and there is almost an endless range of stone varieties offered for the private and public marked. Thus, Europe and the rest of the world are faced today with a rapidly increase of import of materials from other countries. This raises a common need for good methods to evaluate quality and suitability for "unknown" stone materials and to define requirements to ensure satisfactory service life. Common European standards should be of help in this respect, and several standards have been prepared for testing and for natural stone products. The general idea is that these standards shall give information about relevant properties to be tested for different applications and that they may include technical requirements or define different quality classes suitable for different applications. However, this is not the case for most product standards in the area of natural stones. Many product standards do not give this guidance and each country has to define their own requirements. This is also valid for the existing standards for slate and stone products for discontinuous roofing and cladding. Requirements have not been defined in an unambiguous way, and the standard set up a rather comprehensive and costly set of test methods that may be questioned both with respect to suitability for evaluation of technical quality and the relevance for various types of roofing slates. One additional challenge for the Nordic countries, are that the standard does not cover our roofing materials per definition, since it is specified only for very low to low grade metamorphic slates. Research work is under way in order to specify technical requirements, test methods and evaluation criteria that cover Nordic roofing materials, climate and construction technique and that can be used for evaluation of the suitability of all kind of slates for Nordic roofing purposes. The work is also directed towards changes in the present European roofing standard such that also Nordic schists are covered and thus may be used also for CE marking of these products. Results from the project will be presented.
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