Three Portuguese limestones (two grainstones, Semi-rijo and Moca Creme commercial types, and a travertine) were subjected to salt crystallisation test (EN 12370:1999). Grainstones specimens showed higher weight loss than the travertine ones. Results are discussed, using parametric and nonparametric statistics, in relation to pore space characteristics that have been considered durability predictors, evaluated at the macroscopic (water imbibition) and microscopic (mercury injection porosimetry) levels. Several of the pore-space parameters indicate differences between grainstones and travertine, but these differences are much lower than the differences in weight loss. Results of the durability dimensional estimator (DDE) seem to present a discrepancy, with higher values in the rock type having lower weight loss (travertine). Additionally, weathering patterns of travertine samples show marked irregularities (a feature that is not assessed by weight loss). These irregularities are attributed to heterogeneous spatial distribution of detritic components (a feature that is not assessed by pore-space parameters). Comparing the grainstones, Moca Creme showed higher values of mass loss and several durability predictors suggested noteworthy differences in relation to Semi-rijo. However, these differences are much lower than differences in weight loss. Calculated crystallisation pressures are even higher for Semi-rijo. It is proposed that petrographical aspects of Moca Creme, namely heterogeneity related to the presence of bioclasts and veinlets, could contribute to explain the higher weathering susceptibility of this rock type. These results highlight the need to include petrographical features in assessments of durability and the usefulness of visual description on the characterization of salt weathering.

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The present work reviews studies with information on the effects of water by itself on stones of the built environment both to assess the impact of this substance and to discuss possible implications for conservation. The analysis concerns empirical results from previous publications dealing with the effects, on several rock types, of freeze–thaw, wetting, erosion by running water and substances resulting from the water–stone interaction. Laboratory studies have shown that water freezing can cause physical damage even in low porosity rocks. As far as we know, this is the first review that considers comparative laboratory studies of freeze–thaw and salt crystallization on the same rock specimens, and these point to lower erosive effects than salt weathering, as freeze–thaw can provoke catastrophic cracking. Wetting has shown strong damaging effects on some fine-grained clastic rocks. Erosive features have been reported for rain exposition and for some fountain settings albeit, in these field studies, it could be difficult to assess the contribution of pollutants transported by water (this assessment could have meaningful implications for stone conservation, especially in fountain settings). Water also interacts with stone constituents, namely sulfides and soluble salts, releasing substances that could impact those stones. Sulfides are a relatively frequent issue for slates and granites, and our observations suggest that for this last rock type, this issue is mostly associated with the presence of enclaves and, hence, avoiding the surface exposition of such enclaves could solve the problem.

This paper presents a study of stone decay on the Basílica da Estrela, the most famous 18th century monument in the city of Lisbon, Portugal. It was built with Jurassic and Cretaceous limestones from the surroundings of Lisbon. Different approaches were used to establish the typology, causes and processes of the major weathering forms. Limestone samples from ancient quarries, salt efflorescences and disintegrated stone material from the interior of the church were characterized by chemical, mineralogical and petrographical analyses. Limestone physical properties related to fluid percolation were also determined. Detailed surveys of stone decay phenomena were carried out on the monument. Textures of grey-level images representative of the weathering forms were analysed by image analysis through covariance and granulometry operators. An HIDSPEC computational hydrogeochemical model, phase and graphical diagrams, and multivariate statistical analysis were used for water-rock interaction studies. Physical weathering forms prevail inside the church. The yellow Cretaceous limestone is the most deteriorated stone. This observation compares well with its intrinsic properties. The weathering is determined by the stone structures, such as stilolytes and fossils, and architectural features (geometry and surface finish). Soluble salts such as trona and thenardite were only found in a very small area inside the church.

Natural stone is an important component of historical heritage (buildings and art objects such as sculptures or rock engravings), and it is still widely used in contemporary works. Soluble salts are the main erosive agent in the built environment, and we review here comparative studies that subject the same rock type to testing with different salt solutions. The results mostly support the accepted notion of the major impact of sodium sulphate, although there are some exceptions. The effects of sodium chloride and calcium sulphate deserve specific discussion given field information on the relevance of these specific salts in the built environment. We relate the information collected to the issues of risk assessment (considering both geochemical conditions and salt effects) and conservation interventions (highlighting the interest of tests that do not produce damage to susceptible materials) and present some methodological suggestions to avoid a case study culture.