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Salt crystallization is recognized as a major cause of damage to porous building materials, threatening the sustainable preservation of our valuable built heritage. Unfortunately, the crystallization behavior of the detected salt mixtures is complex and not fully understood. While the deliquescence points of single salts are well documented, this is not the case for salts in a mixture where one is confronted with the presence of different cations and anions. In this paper the salt content of the murals and the limestone tracery of the main entrance porch from the sixteenth century church of St. James in Liège, Belgium is investigated and related to the climatic conditions of its environment. Concerning the salt load, the research consists of hygroscopic moisture content measurements, quantitative ion analyses, and the prediction of phase equilibria using the thermodynamic model ECOS/RUNSALT. This model can predict the salt crystallization sequences of a particular ion mixture. The output is mathematically evaluated with collected temperature and relative humidity data, which enables the calculation of the number of salt crystallization–deliquescence cycles. The results show that even small amounts of salts can cause damage over a long period of time when the environment causes frequent cycles of crystallization–deliquescence over time. It is shown how a mixture of small amounts of (double) salts, including hygroscopic ones, can have a significant effect on the decay of historic building materials in the case of daily changing climatic conditions and periods of extreme drought. As a result, the crystallization of double salts and hygroscopic salts such as calcium nitrate cannot be ignored. The scientific method and the results are described. [ABSTRACT FROM PUBLISHER]

Different grouting and repair mortars were developed and evaluated for the conservation and restoration of fragmented bricks in the walls and floors of the remaining cellars underneath the Aula Magna, the palace's main banqueting hall, and to fill the lacunae and perform edge repairs of red and blue-grey ceramic floor tiles in the remaining cellars underneath the chapel of the former Palace of Coudenberg in Brussels, Belgium. To prevent the deposition of lime bloom at the surface of the masonry and to achieve an acceptable colour match of the grout in harmony with the bricks of the Aula Magna, the effect of brick powder added to natural hydraulic lime was studied. The pozzolanic properties and colour match of several historic and modern powdered bricks were investigated. Surprisingly, ancient bricks do not seem to possess higher pozzolanic properties than the more modern ones, although it is supposed that they were fired at lower temperatures. Additional evidence for the pozzolanic reaction of the different brick powder materials was obtained from a simple visual observation of stored samples. After eight weeks all of the samples containing brick powders, fired at low and high temperatures, added to putty lime had hardened under water and were transformed into a remarkably tough material. These results are important, as modern bricks are readily available in large quantities and different colours, which are hence in favour of being used instead of historical material from the site. For the repair of the ceramic floor tiles different mortars were investigated with mixtures containing talcum, stone or brick powder, pigments, and chalk added to an epoxy binder. The mortars were tested in the laboratory and in situ for their workability and resemblance with the historic floor tiles. The finished mortars showed excellent aesthetic properties with the tiles in situ and good properties to prevent further loss due to human interaction. [ABSTRACT FROM AUTHOR]

Over the last twenty years, more research has been conducted on the application of nanolime as a consolidant. However, a limitation in consolidation with nanolime is the back-migration of the product to the absorption surface during the drying phase, resulting in insufficient product deposition in depth. In this paper, a solvent composition is adapted to the substrate properties to examine the theory that a nanolime with low kinetic stability should be applied to prevent back-migration to the absorption surface for a substrate with large pore size. The common solvent composition of 100% ethanol has a kinetic stability considered too high. Nanolime dispersions (CaLoSiL® E 20 g/L) with different ethanol:water (100:0, 95:5, 90:10, 80:20) ratios were tested on lime mortar samples. The treated samples were subjected to several test methods to evaluate the effectiveness of the consolidation treatment. After comparing the results, the theoretical propositions were substantiated: a back-migration was noticeable in samples treated with the nanolime containing 100% ethanol, while no back-migration was observed in the other solvent compositions. Samples treated with a nanolime dispersion with the addition of 10% deionised water showed promising results regarding mechanical strength, product deposition over the entire depth profile of the sample, and porosity properties. [ABSTRACT FROM AUTHOR]