Abstract:

The material defined as “artificial stone”, frequently used on the façades of the late 19th and early 20th century buildings, is a mixture of binder, aggregate and other additives, and consists of flat plaster coatings applied in-situ and architectural elements with decorative reliefs, some of which may be load-bearing and which may be produced with different types of moulds either in-situ or precast at the workshop. One of the effects of the Industrial Revolution in the 19th century was a tendency to standardize architectural production, which in turn moved away from time-consuming and costly traditional techniques in search of those in accordance with the dynamic social, economic and cultural structure of the period. Early modern scientific understanding of binders with hydraulic properties at the end of the 18th century and the development of new methods for their artificial production in early 19th century supported this new material and technique. Turkey and more specifically Istanbul, located on the periphery of these developments in architecture, techniques and materials was also affected contemporaneously. However, it is only partially possible to trace this transformation in publications and archive material. The main sources of information are the period buildings themselves. Thus, the use of artificial stone was evaluated with reference to architectural, material and application characteristics. Field-work enabled the selection of ca. 30 buildings for sampling and the number was reduced to 15 in the final stage, focusing on those buildings reflecting the characteristics of their period. Samples were taken from various types of artificial stone used in architectural programs of different styles. The experiments, conducted according to related national and international standards based on research programs recommended for similar mortar and plaster samples in literature, enabled the determination of the physical, raw material and mineralogical characteristics of the samples. Results indicate that all the binders have hydraulic quality, some being artificial cements and/or natural water limes and others being fat limes mixed with mostly artificial pozzolanic additives, such as brick dust and ash, charcoal or slag as well as some natural pozzolanas such as opal. Some of the limes included magnesite, which is known to enhance the mechanical properties, whereas the identification of calcium sulphate in XRD and SEM-EDX analyses enabled the identification cements, as this additive is known to have been used since the 1850s to regulate the setting characteristics of these binders. Those including higher ratios, on the other hand, may be identified as calcium sulphate based binders, which appear frequently in literature. The physical characteristics of the plasters are somewhat different, compared to similar mortars and concretes: The densities and binder/aggregate ratios are generally higher, porosities are lower and the size of the aggregates is smaller. The plasters may have single or multiple two to three layers. As it may be expected, compared to the lower rough layers, the upper finishing layers are denser, have higher binder/aggregate ratios and include aggregates smaller in size and usually lighter in colour, such as white sands and lime stones as well as marble pieces in some cases. Fibrous aggregates as well as artificial aggregates with pozzolanic qualities are used in almost all samples, including those with hydraulic binders, indicating a continuity of tradition and/or distrust in these new materials.

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