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Organizers: - The Technical University of Denmark; - The National Museum of Denmark; - Building Heritage of Denmark; - Palaces and Properties Agency; - The Royal Danish Academy – School of Conservation. The conference was scientifically sponsored by RILEM and financially by Knud Højgaards Fond. The conference 'Salt Weathering on Buildings and Stone Sculptures' addressed the complex problem of built heritage and stone sculpture deterioration due to salts action and consequently the assessment and development of conservation procedures. The event was hosted by the National Museum of Denmark, having as organizers the Technical University of Denmark, the National Museum, Building Heritage of Denmark, Palaces and Properties Agency and the Royal Danish Academy – School of Conservation and took place in last October, in Copenhagen. Besides the optimal meeting venue and other facilities the National Museum of Denmark comprises, a new exhibition concept with interactive workshops was experienced. Conservators were moving into the museum’s large exhibition hall, where functioning workshops were giving visitors a unique opportunity to "look over conservators’ shoulders". This was a great chance for the large public to ask questions and thus discover the hidden side of conservation profession, analytical methods and materials. The conference in Copenhagen successfully brought together a broad range of scientific contributions and case studies in a multifaceted effort to fill up the gap between theory and practice; the situations in practice are much more complex than usually assumed by the theoretical models. Salt weathering represents one of the most important concerns in the field of building conservation (including mural paintings or/and sculpture decoration), from both damage as well as treatment complexity point of view. Therefore, the conference followed up closely the ways of enhancement of desalination treatments efficiency, derived from case studies with the support of laboratory experiments. The three days conference was divided in sessions which covered all the important topics regarding salts deterioration issues within built heritage or stone sculpture. Starting with the mechanism of Decay and Transport of Salts the topics moved to Materials analysis and diagnosis of damages in the second day and ended with Hands on Conservation and Methods of repair. The conference began with "A review of salt transport in porous media, assessments methods and salt reduction treatments", a presentation given by Alison S. Heritage from Cologne University of Applied Science (Germany). It was a key note presentation, describing the current scientific understanding of salt and moisture transport processes and the extent to which this knowledge can bring feedback into the practical arena, to aid the conservator. In the section Transport of salts the European project "Desalination" was presented by Anne Bourges from Laboratoire de Recherche des Monuments Historiques (France). Five case studies done at Saint Philibert Church in Dijon, which were illustrated comparing the effectiveness of desalination systems (poultices), strongly underlined the close link between the effectiveness of desalination treatments and the proprieties of both stones and poultice materials. Connected with the first topic of the conference, another very interesting research regarding the wind speed factor in salt damage in general and salt damage at Petra monuments in particular, was presented by Dr. Fadi Bala’awi, Hashemite University, Zarqa-Jordan. The research was done to evaluate the role of wind speed in salt crystallization and distribution. It presented a detailed monitoring of the microclimate condition and its role in the salt distribution at selected monuments in Petra, in order to understand the extent and mechanism of salt damage. The results have shown the importance of including the wind speed factor in salt weathering simulation tests, since both the salt decay rate and the salt distribution were found to vary significantly at different wind speed conditions. The deterioration of porous building materials due to crystallization of salts within their pore structure is a wide spread weathering process and the main cause of decay. The contributions regarding the decay phenomenon covered many important issues; some well known but seen in a new light were better understood and new treatment solutions were experienced. Barbara Lubelli from Delft University of Technology Netherlands) talked about "Sodium chloride damage to porous building materials: effect of RH changes", emphasizing the importance of the study of damage evolution in practice in order to better understand the damage mechanism. The case studies presented were performed both in situ and in laboratory, demonstrating the relevance of dissolution/crystallization cycles for the development of sodium chloride damages. The high frequency of RH changes causes fast damages in reality, while in the laboratory tests, where factors such as capillarity moisture, and drying at constant temperature and RH are adopted, very little damage was observed. For a better vision of the damage mechanism, ESEM analysis were performed on cross-sections which led to the hypothesis that the mechanical interaction between salt and pore wall would be enough to generate stress and thus damages. For more verification a crystallization inhibitor was added and was observed that salts are crystallizing but do not cause damage because there is no adherence to the pore wall. Experiments done on crystal growth under a constraint in strictly controlled condition were presented by Julie Desarnaud from CINaM, CICRP Marseill (France). The results show that the loaded faces of a crystal immersed in a supersaturated solution are dissolved and therefore the crystal is both unable to grow against the applied constraint and to develop any 'crystallization pressure'. Ioannis Ioannou from University of Cyprus studying salt crystallization in natural building stones reached the conclusion that due to the fact that the cryptoflorescence is considerably more damaging than efflorescence, the treatments with water repellents can actually have a harmful effect on the treated materials. Usually the water repellents are used to protect the surface of stones from contaminants, but the paper demonstrates the opposite. Actually those treatments can promote the masonry decay by suppressing the capillary transport of water and salt solution to its surface, thus forcing the formation of cryptoflorescence. Thus, the use of surface treatments may cause significant crystallization damage to the masonry in the long term, as inevitably some water will gain access to the masonry structure and will be lost by evaporation from the surface, leaving salts behind. This finding is particularly important and should be taken under consideration in practical situations where the prevention of efflorescence, which sometimes is also very important – in case of decorative masonry - must be very well adapted to the necessities, being aware of this risk. The first conference day was ended in a pleasant atmosphere during the reception offered at Thorvaldsen Museum, Denmark’s oldest museum, surrounded by Bertel Thorvaldsen sculptures and good wine. It was a chance for the participants to get to know each other and prolong the discussions started during the day. On the way to the reception venue I had the opportunity to take part in a short ad hoc 'tour' of Copenhagen’s monuments, their history and salt weathering problems, guided by Tim Padfield, an internationally well known specialist of microclimate in museums and historic buildings, who was part of the scientific committee of the conference. The second day brought the participants together again for discussing the topic of Material analysis and diagnosis of damage. I will only mention here some of the papers that have been presented, trying to highlight the main ideas passed on by the conference, being difficult to condense all the information into a simple review. Furthermore, the organizers published a book of proceedings where all the papers presented at the conference are available. Non-destructive methods were lately implemented for different heritage preservation analysis or monitoring necessities. M. Gomez-Heras from Queen University of Belfast (UK) presented his research through high definition (HD) laser scanning for the evaluation of laboratory simulations of building limestone salt decay. Tests comprised measurements of the surface morphological changes during alternating cycles of simulated salt weathering of lime stone, demonstrating the potential value of this non-invasive technique in adding new spatial information to patterns of surface weathering and erosion. One example given by the author was the possibility of monitoring the subtle changes like pores filling and surface swelling during early-stage weathering that are not detected by traditional parameters such as weight loss. Isabelle Brajer from the National Museum of Denmark emphasized how ‘imperative climate control is in salt reduction treatments which are not long lasting without subsequent monitoring’. Her study comprised a re-evaluation of the desalination treatments done in Tristed Church (Denmark) nine years ago which revealed the reversion of the problems as they were prior to the treatment. This is one of the major problems of massive monuments still in function which being salt contaminated need a careful assessment of the salt weathering degradation in concordance with climatic control. Unfortunately, sometimes conservator’s recommendations are hard to implement in monuments which are still in use and are not understood by the community in charge of their maintenance. Two studies highlighted the importance of the attentive analysis of the environmental characteristics of the salts nature and transport which can give sometimes the best solutions for salt management approaches. Andrew Thorn, in his paper ‘Salt management within rock art shelters’, gave two examples of interesting ways of approaching the salt related damages in painted rock art sites from Australia, where they cannot be isolated but only handled. In the first case study the diagnosis itself became the treatment; only the assessment of the extent and movement of the salt contamination areas in relation with the painted surface in danger at repeated intervals showed the evolution in time and in this case, the risk diminishment. In the second case study the diagnosis of the salt mechanism revealed that it was thermally determined and that a simple shading of the site (planting trees) would stop the mechanism. A study regarding the 'Weathering of the Cathedral at Kirkjubøur, the Faroe Islands', presented by Poul Klenz Larsen from the National Museum of Denmark, Department of Conservation, showed also the importance of understanding the material degradation in connection with the climatic environment. In this example, the ruins of the church were temporary covered with a special shelter which would protect the structure against driving rain, but studies of salt mechanism in connection with the local environmental climate bear out the possibility of aggravating the salt decay. Therefore the conclusion was that the walls would best be kept wet and just a traditional maintenance of the mortar joints would ensure the mechanical stability of the structure. Regarding the last section of the conference, Methods of repair, I would like to refer to at least two of the contributions with interesting new projects regarding salt treatments. A very interesting research was presented by Eric May (School of Biology Science, Hampshire, UK) regarding 'Bioremediation: potential and challenges for stone treatment'. The use of microorganisms to help preserve, protect and restore building stone is a new technology that offers a different approach supplementing the existing conservation technologies. Although biomineralisation has been observed for many years, the potential for its use in stone consolidation has only been explored relatively recently. Biocalcifying bacteria have been used to successfully promote carbonatogenesis on the surface of lime stone buildings or statuary and this type of newly formed carbonate is shown to be resistant to mechanical stress. Recently, microorganisms have also been used to remove sulphate from black gypsum crusts. The EU project BIOBRUSH (Bioremediation for Building Restoration and the Urban Stone Heritage) linked the mineralization process that removes stone crusts to consolidation by biomineralisation. A new mortar system incorporating nitrate-reducing bacteria capable of removing nitrates was also developed and described during the conference. Lisbeth M. Ottosen and Inge Rörig-Dalgaars from Technical University of Denmark, Department of Civil Engineering, presented two of their researches regarding the "Electrochemical removal of salts from masonry" and "Desalination of a wall section with murals by electromigration". For the first project mentioned above, new electrode units were developed for desalination of brick masonry and were tested afterward, in a pilot scale experiment on a salt contaminated building. The chosen building was tainted with sulfate in a high concentration; chloride and nitrate were less present but in dangerous concentrations at some points. The obtained results were very good; the new electrode units buffered the acid produced at the anode and the contaminating ions were accumulated within the units during treatment and removed afterward from the site together with them. In the applied electric field, chlorides and nitrates were efficiently removed. Sulfates did not decrease radically during the 4-month treatment (possibly due to their low dissolution rate) but it was expected to continuously decrease over longer duration. Regarding the second experimental work, the application of the electrokinetic method was investigated for the removal of sodium chloride from a wall section with murals. A current of 2.9mA/cm was used for a two weeks treatment. The chloride was reduced from the wall section and accumulated in the removable poultice placed between the wall surface and the electrodes. During the electrokinetic treatment, the desalination effect was assessed by measuring the chloride content in the removed poultice and in drilling samples from masonry. The drilled samples were made prior to and after the experiment to investigate the changes for chloride and also the pH in the wall section. No pigment changes were visually observed after the treatment. The pigments from the murals are hardly soluble at neutral pH, which during this experiment was very closely measured and no changes were observed. This method has big potential for murals future treatments, the only mentioned necessary improvement being the evenly distribution of the chloride reductions on large scale which could be achieved, apparently, by managing better the wetting process. Besides the oral presentations, the conference had also a poster section covering again the complex conference’s topic with interesting aspects regarding salts weathering phenomena, analysis and treatments. An interesting side of the conference, besides the high level of researches and results, was the fact that almost all the studies presented had also a practical side and most of them were already tested not only in specialized laboratories but also in situ or if not yet, this was the next step. This successful event was possible due to the professionalism of the organizers which knew very well how to merge science and art in relation to heritage preservation, gastronomic breaks and practical site seeing. The participants were privileged to visit the Kronborg Castle (known as Hamlet Castle) which is undergoing restoration and rehabilitation works, Fanefjord Church where the mural ensemble dating from about 1550 suffered severely from salt decay and is presently the subject of a high standard conservation project and some other heritage monuments damaged by salt from Copenhagen. The high number of participants from 21 countries made the conference even more interesting from the point of view of its diversity.Interdisciplinary topics were enhanced by the variety of nationalities and specialisms, showing sometimes different approaches or similarities where you don’t expect, but all leading to an improvement of the future treatments and preventive measures efficacy. The importance of this topic and the success of the conference were ascertained by the agreement for a following conference that will take place in Cyprus, organized by the University of Cyprus. ▲TOP To save this article please Download this article
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