Abstract Most historic stone monuments in Bratislava (Slovakia) are built with various types of porous, light and weakly cemented sedimentary rocks. These Neogene sandstones and limestones, also known as Leitha limestones, were quarried in the Vienna Basin. The various sedimentary environments are reflected in the heterogeneity of lithotypes and their cementation. The distinctly different pore structure of these rocks is reflected in their very variable physical properties and consequently in the distinct durability. Petrographic and petrophysical properties were determined on main ashlar types of the two most important historical monuments of Bratislava, the Castle and St Martin's Cathedral. Fresh samples of Leitha limestones were also obtained from the existing or abandoned quarries. The study includes a detailed petrographic examination of major rocks types and an assessment of their mineralogical composition by X-ray diffraction and microscopy. Hygric properties and porosity influence the weathering stability and the chances to apply conservation treatment. Parameters such as pore volume, pore size distribution by mercury porosimetry, specific surface of pores by nitrogen adsorption (BET) analysis as well as water sorption, capillary water uptake and drying behaviour were measured and compared for the six studied lithotypes.

Abstract Rhenish tuffs from the volcanic Eifel region in Germany, in particular the so-called Römer tuff, are among the most prominent and voluminous natural stones in Dutch monuments. The Römer tuff has been used since Roman times, and was widely used again in Romanesque (and to a lesser extent Romano-Gothic and early Gothic) architecture. The limited (or non) availability of Römer tuff for restoration purposes is posing an increasing problem. Last decennia, the availability of Römer tuff was practically limited to blocks from the lower parts of the pyroclastic flows with abundant basalt (and other) xenoliths, giving the rock a different appearance from its traditional type; the different types of Römer tuff also demonstrate different physical and hygric properties. Given the wide use of tuff stone in Italian architecture, several Italian tuffs have been evaluated in search of a compatible replacement stone for Römer tuff. The replacement stones should approach the original as much as possible, that is, in terms of authentic appearance, physical characteristics and durability. The Italian tuffs evaluated include tuffs commercially denominated as Tufo Etrusco and Tufo Romano (from the central part of Italy) and a variety of Neapolitan Yellow Tuff (Naples region). Hygric behaviour, resistance to frost-thaw cycles, petrographic characteristics and mineralogy of Italian tuffs have been determined and compared with original Römer tuff. In all three cases, resistance to frost-thaw cycles is unfortunately shown to be considerably less than that of original Römer tuff. In addition, hygric expansion of the Neapolitan Yellow Tuff appeared to be considerably larger than that of original Römer tuff. Of the tuffs evaluated, the variety of Neapolitan Yellow Tuff is a good match with the original Römer tuff in terms of visual appearance. It has already been sparsely used in the Netherlands in minor amounts. However, the durability characteristics require additional evaluation.

Abstract In west Austria Quaternary building stones, such as lithic breccias of alluvial fans and talus slopes or calcareous spring tufa, have been frequently used as building stones since Roman times. Spring tufas are a widely used building material of historical objects in west Austria. This porous calcareous rock, formed by carbonate precipitation from calcium carbonate supersaturated spring waters, is an appreciated building stone: easy to quarry, lightweight, easily workable and relatively resistant to weathering. The Hötting Breccia, a lithified talus and alluvial breccia, has only been extracted in a few quarries near Innsbruck/Tyrol, however. Many of the mediaeval buildings of the towns of Innsbruck and Hall are built of this decorative type of stone. Petrography, mineralogical composition, porosity parameters and hygric properties have been investigated in this study from two tufas and one breccia occurrence. The results obtained reveal that these Quaternary stones, being formed at the Earth's surface, exhibit pore properties and hygric behaviour which differ considerably from other stone materials which have been subjected to the physical-chemical formation conditions of the upper Earth crust. This has implications for their workability, internal stability and weathering behaviour.

Abstract Salt crystallization in the pore spaces of building stones can produce significant deterioration. The properties of the salt solution, the salt phases and the climatic conditions, as well as the rock fabric, significantly influence the state of rock weathering. To examine the influences of rock fabric and salt type on salt weathering, detailed investigations were performed on three sandstones. The fabric (mineralogical composition, grain size, etc.) and the petrophysical properties (porosity, pore-size distribution and hygric dilatation) of the sandstones were analysed and correlated with length changes during cyclic salt loading. The salt tests were carried out with two different salt types: (i) sodium sulphate and (ii) sodium chloride. The observed length changes differ for the investigated sandstones. Contractions of the samples, as well as a pronounced residual strain after the applied salt cycles, were observed. Specific deterioration features can be determined for the sandstones independent from the salt types used. However, the decay mechanisms, which lead to a significant deterioration, are different for sodium sulphate and sodium chloride. For sodium sulphate, a strong expansion occurs during the solution uptake cycles. This expansion can be attributed to hydration pressure during the transition from the water-free thenardite to the hydrate phase mirabilite. In contrast, the samples in the sodium chloride test show the main expansion in the drying stage. This can be related to the crystallization pressure caused by the growth of halite.

Abstract The deterioration of three marbles (Palissandro, Sterzing and Carrara) differing in composition and rock fabric has been studied using measurements of the thermal dilatation in the temperature range from −40°C up to 60°C. A long-term freeze–thaw experiment was performed to characterize the frost weathering via Young’s modulus. The results show that the combined effect of heating and cooling under dry and water-saturated conditions significantly influences the material properties. The thermal dilatation and its anisotropy can be explained by the crystallographic preferred orientation of calcite and dolomite as well as with the thermal expansion behaviour of these minerals. The residual strain, i.e. the permanent length change, after thermal treatment is different for the investigated samples and less pronounced for the dolomitic marble from Palissandro. The hygric expansion is of only minor importance and weak in the phlogopite-bearing Palissandro sample within the direction parallel to the foliation. Fresh and artificially weathered marbles were exposed to 204 freeze–thaw cycles. The Young’s modulus for the Carrara marble decreases from 55 GPa to 28 GPa while the porosity increases from 0.25% to 0.62%. The effect on the Palissandro and the calcitic Sterzing marbles is less pronounced while the artificially weathered ones clearly exhibit a drastic reduction in Young’s modulus. The progressive loss in strength is caused by progressive microfracturing or the loss of cohesion along grain boundaries due to the crystallization pressure of ice growth. The experimental data along with existing theoretical models lead to the conclusion that the physical weathering of marble is influenced by cooling and heating under mid-European climatic conditions.

Abstract The palace of Nuevo Baztán is a state-designated historic monument in central Spain built in the early eighteenth century. The main building material used in its facades is limestone. The aim of this investigation was to characterize the limestone, defining deterioration mechanisms contributing to the decay of the stone facades and testing a series of potential preservation treatments. The limestone is a biosparite; two microfacies were identified according to microscopic differences (limestones A and B) with distinct petrophysical characteristics mainly due to their different pore systems. Primary deterioration mechanisms were identified as those related to cycles of thermal and hygric stress, biodeterioration and those associated with structural movements. Main decay forms in the surface of the stone are erosion with material loss, spalling and flaking, chromatic alteration, fissures and biodeterioration. Conservation products prossessing water-repellent properties were therefore considered. From an initial selection of ten products, two siloxane-based products were ultimately determined to be the most effective on the basis of chromatic variables, water vapour permeability, water-stone contact angle, scanning electron microscope observations and durability (artificial ageing tests). Both products reduce water absorption rates and are expected to slow the rate of limestone decay. This study also demonstrates the value of advance testing of potential treatment methods before application in the field.

Abstract Germany has an enormous number of different carbonate rock units, which vary widely in their geological age and sedimentary depositional environment. Limestones quarried from these exposures have a wide range of usages and applications, such as dimension and ornamental stones, floor tiles and panelling, and for use as paving stones and massive stones. Since antiquity, limestones were used as building materials in areas where they were naturally available and abundant. Limestones exhibit a relatively good weathering resistance, which is mainly controlled by the mineralogical composition and the rock structure. The susceptibility of limestones to weathering and alteration is only secondarily related to the stone's contact with rainwater and its exposure to frost. In this situation the pore space is the main controlling factor. Industrialization and the subsequent increase in air pollutants, which started at the end of the nineteenth century, led to the formation of dark and unsightly crust deposits on the limestones surfaces. These crusts, being the result of man-made activities, are the main weathering problem for carbonate dimension stones.

Abstract This study deals with the design of two hydrophobic hybrid SiO 2 –TiO 2 materials and their application in the field of monument conservation. The nanocomposite consolidants were based on the modification of tetraethoxysilane (TEOS) with the incorporation of both TiO 2 nanoparticles and hydroxyl-terminated polydimethylsiloxane (PDMS). The TiO 2 nanoparticles have been prepared from the hydrolysis of titanium tetraisopropoxide (TTIP) in the presence of oxalic acid as a catalyst. The physico-chemical properties of the designed hydrophobic nanocrystalline SiO 2 –TiO 2 –PDMS composites have been extensively studied before their application as consolidants on a limestone. Overall, the effectiveness of the nanocomposites was evaluated by the comparative characterization of untreated and treated stone specimens. The results of both capillary water absorption and contact angle measurements point out that the TiO 2 –SiO 2 –PDMS nanocomposites functioned as hydrophobic coatings. Furthermore, the results obtained from microdrilling resistance and Fourier Transform Infrared spectroscopy (FTIR) revealed a penetration depth of the nanocomposites within the stone of c. 15 mm. The innovation of these syntheses pertains to the application of hydrophobic semi-transparent and transparent nanocomposites with self-cleaning and strengthening properties, without altering the colour of the stone surface and the water vapour permeability.

Abstract The weathering of historical buildings, as well as that of any monument or sculpture using natural stone (or man-made porous inorganic materials) is a problem identified since antiquity. Although much of the observed world-wide destruction of these monuments can be ascribed to war and vandalism, many other factors can contribute significantly to their deterioration. These threaten the preservation of the current inventory of historically, artistically or culturally valuable buildings and monuments. Furthermore, a drastic increase in deterioration has been observed on these structures during the past century. This prompted Winkler (1973) to make a pessimistic prediction, that at the end of the last millennium these structures would largely be destroyed because of predominantly anthropogenic environmental influences. Fortunately, this has proven not to be the case. There is a general belief that natural building stones are durable, and not for nothing does the Bible refer to the Rock of Ages. However, all rocks will weather and eventually turn to dust. If rocks are cut and used in buildings, the chance of deterioration increases because other factors come into play. To understand the complex interaction that the stone in a building suffers with its near environment, (i.e., the building, and the macro environment, the local climate and atmospheric conditions), requires an interdisciplinary approach with the work of geologists, mineralogists, material scientists, physicists, chemists, biologists, architects and art historians. Although most historical buildings use natural stone as the main construction material, other materials, such as mortars for masonry or rendering and ceramic