Per Storemyr The Stones of Nidaros An Applied Weathering Study of Europe's Northernmost Medieval Cathedral Dr. Ing. (Ph.D.) thesis no. 1997:92 Department of Architectural History Norwegian University of Science and Technology Trondheim, Norway Original printed edition 1997 Layout by Per Storemyr ISBN 82-471-0128 ISSN 0802-3271 This edition: Slightly edited and prepared for PDF 2010 Per Storemyr The Stones of Nidaros An Applied Weathering Study of Europe’s Northernmost Medieval Cathedral Thesis submitted in partial fulfillment of the requirements for the degree Doktor Ingeniør by Per Storemyr Department of Architectural History Norwegian University of Science and Technology Trondheim, Norway 1997 For Fränzi But we cannot avoid remaking our heritage, for every act of recognition alters what survives. David Lowenthal “The Past is a Foreign Country” Preface When I was introduced to the field of stone weathering and stone conservation as a geologist in 1990, I saw black gypsum crusts formed as a result of air pollution everywhere. This was in my happy days as a politically correct environmentalist and represented the “one-dimensional phase” of my career as a stone weathering scientist. Two dimensions appeared somewhat later as I realised that various stone types behaved differently and that black crusts were very unevenly distributed on the walls of Nidaros cathedral (Trondheim, Norway) which is the building used as a case study in this thesis. Realisation that a cathedral, like any building, is a three-dimensional or spatial system, new perspectives became apparent. It also became clear that this spatial system heavily interacted with the climatic conditions in the Trondheim region. The weathering of the cathedral became much more complex than first thought. However, the great qualitative leap forward occurred on realising that the cathedral had a history back to the Middle Ages and that thousands of skilled and unskilled people had built, restored and rebuilt the church. When time and people entered my scientific world, I became so interested in weathering studies that I started to work on this thesis. It was fascinating that there were a great many relationships between weathering phenomena, history and how people interact with a cathedral. My aim was to explore such interactions in order to make a scientific contribution to the field of conservation of historic stone buildings. I also wanted to give the cultural heritage authorities, particularly those responsible for the condition of Nidaros cathedral, a better and broader basis for strategic planning, risk analysis and conservation measures. It would have been impossible to explore these relationships without considerable co-operation and help. Prof. Knut Einar Larsen at the Department of Architectural History, Norwegian University of Science and Technology (NTNU), Trondheim, offered in 1991 to be my main supervisor and kindly helped me establish the formal framework. Since the content of the thesis gradually moved away from his area of expertise, Dr. Andreas Arnold at the Institute for Preservation of Historical Monuments and Sites (Institut für Denkmalpflege), at The Swiss Federal Institute of Technology, (ETH), Zurich, has in practice, although not formally, been my supervisor over the last five years. I am most grateful for his intellectual guidance and friendship, and that I could work, whenever I wanted, in his laboratory. My sincere thanks also go to the head of Institut für Denkmalpflege, Prof. Georg Mörsch, for receiving me as a student and scientist at ETH. The Restoration Workshop of Nidaros Cathedral (RWNC) under the leadership of Cathedral Architect Arne Gunnarsjaa and later Director Øivind Lunde has also made a significant contribution to this thesis. Firstly, by allowing complete access to every corner of the building; secondly, by letting me search all archives; and finally, by offering me a position as a conservation scientist at the workshop. Thus, I have become rather familiar with the cathedral, which was a prerequisite for this thesis. The work was carried out at the three institutions mentioned above. Department of Architectural History and Institut für Denkmalpflege were my bases in 1992/1994 and 1993, respectively, and since 1995 I have been fully employed at The Restoration Workshop. In addition to the people mentioned above, I have received qualified scientific and personal help from several others at these institutions: At the Department of Architectural History, Staale Sinding-Larsen and Dag Nilsen have commented upon earlier drafts of parts the thesis, especially related to theory and method. Ellen Woldseth and Astrid Presthus have provided a safe haven at the institute and generously helped me with all practical details. At the Institut für Denkmalpflege, Konrad Zehnder shared his wonderful way of observing and describing weathering phenomena during extensive illuminating visits to monuments in Switzerland. He and Andreas Küng also patiently tried to answer all my many questions concerning soluble salt analysis, which was carried out at the institute. I would also like to thank the people at the laboratory for conservation research and technology at the Swiss National Museum, located with Institut für Denkmalpflege, for their help. At The Restoration Workshop, several individuals have been directly and indirectly involved in my work, many of whom have given me invaluable practical help and insight into craftsmanship and traditions at this 130 year old institution. I am particularly indebted to Erling Refseth who helped so much in the early phases of the work, Øystein Ekroll who taught me about building archaeology and v history and also commented upon the historical part of this thesis, as well as Geir Magnussen who widened my knowledge about mortars and commented upon the mortar chapter. Atle Elverum helped with surveying and mapping the chapter house, while former restoration architect Torgeir Suul copied several old photos from the rich archive of The Restoration Workshop (ARW). Observation and explanation of weathering phenomena in the old soapstone and greenschist quarries of the cathedral constitute an important part of this work. I have had many fine field trips with Tom Heldal at the Norwegian Geological Survey; he has also commented upon the stone weathering section of this thesis. Lisbeth Alnæs at my former employee, the Foundation for Scientific and Industrial Research (SINTEF) in Trondheim, also gave significant help as we worked together with dimension stone and stone weathering in the early phases of this thesis. The x-ray laboratory at the Department of Geology and Mineral Resources Engineering (NTNU) provided many stone analyses, while the Norwegian Building Research Institute (NBI) in Trondheim generously undertook specific accelerated weathering tests. Although this thesis primarily deals with Nidaros cathedral, I have travelled extensively throughout Norway and the rest of Europe in order to observe old stone buildings and gain experience about how they weather, and participate at conferences. I have met colleagues and friends who were ready to share their knowledge with me through discussion and practical work. In Sweden, Runo Löfvendahl at the Central Board of National Antiquities followed my work and commented upon drafts and final parts of the thesis over the last 5-6 years. We also undertook several field trips and I especially wish to highlight some weeks on the island of Gotland in 1992. At Gotland I was also for the first time introduced to practical stone conservation by Swedish conservators. In Germany, Esther von Plehwe-Leisen (Cologne) and Eberhard Wendler (Munich) realised that we had common interests as they were involved in conservation of soapstone monuments in Brazil. They helped with specific material analysis and skilled interpretation of weathering phenomena. Bayerisches Landesamt für Denkmalpflege in Munich should also be mentioned as I spent some useful weeks with its staff studying conservation projects in Bavaria in 1992. During my work I have also been lucky to have been supervisor for two candidates, Margrethe Moe and Sander Solnes, at the School of Conservation at The Royal Danish Academy of Fine Arts in Copenhagen. They have made extremely good partners for discussion over the last few years. Towards the completion of this thesis I had a serious problem finding someone to correct my relatively poor English. Francis Witkowski at the Department of Geology, Royal Holloway, University of London came to my aid. This thesis would have been unreadable without his careful corrections. To him, all those mentioned above (as well as those too numerous to mention): Thank you! A thesis cannot be written without funding. The Norwegian Research Council, with its three years scholarship (1992-94) and funding for one year at ETH, carried the heavy financial burden. The Restoration Workshop also contributed a great deal, especially as I could use much of my time at work to write. In addition, NTNU and the Directorate for Cultural Heritage (Oslo) contributed. I am most grateful. This thesis is dedicated to Franziska Rüttimann who entered my life just before this work began. She has inspired me and helped significantly with ideas, suggestions and corrections. More importantly, she has kept up with me during these, at times, turbulent years. Needless to say, I am happy to be with you. Trondheim in July 1997 Per Storemyr vi Abstract The deterioration of Nidaros cathedral, Trondheim, Norway has been studied to obtain a basis for adapting conservation measures to be concentrated on zones at risk. Subdivided into six parts, this thesis focuses especially on weathering of masonry and stone decoration, as well as on the historical aspect of weathering, which is embedded and highlighted in a more general weathering context. This so-called “soapstone cathedral” is studied from the original building period in the Middle Ages, via decay and neglect in the post-Reformation period and the gigantic restoration works between 1869 and 1969, to the present condition. The thesis may not only interest cathedral conservators, but also scientists working with weathering and conservation of historic stone buildings.