Conservation of the Built Heritage: Façades
As a frequently seen conservation practice, repair works on the facades aim to carry heritage buildings safely into future by repairing the outer layer of the building that is heavily exposed to environmental factors.
Natural stone is the main building material in many surviving heritage properties in Turkey. Either as a major component of the masonry walls (as dimension or rough stones) or as a surface cover on a masonry wall, stone elements face natural and human-induced deterioration factors from the beginning of the construction phase. A broad range of deterioration agents can threaten the integrity of historical materials and facades, which are highly open to external factors. Conservation actions with the intent of preserving the integrity and authenticity of a property may cause irreversible damage and loss of material if they are based on wrong observations. For this reason, façade conservation works should be carried out under the guidance of a conservation report prepared by conservation specialists.
The most common types of deterioration in stone facades include, but are not limited to:
• Cracks; may occur due to the structural load on the material, climatic effects and corrosion of metal elements, all interacting with the lithological properties of stone, and they can be seen as micro cracks, fissures, crack networks or structural fractures.
• Erosion of joint mortar; is seen on stone and brick masonry and cause further damage on architectonic elements.
• Efflorescence and subflorescence; are formed as a result of the evaporation of water within the structure and hence the accumulation of water-soluble salts on the surface, in the pores and cracks of the material. The use of faulty mortar ingredients as well as the environmental factors (wetting-drying cycle, minerals in the soil, sea salt aerosols, animal wastes and antifreeze salts etc.) play an important role in these formations. The most common salt types contain sodium, potassium and magnesium.
•Crust formations and encrustation; are formed on the surface and create a different morphology and colour than the stone. Crusts are formed by the interaction of acidic gases caused by air pollution with the minerals in the stone and include exogenic deposits. Encrustations are the accumulation of the dissolved material coming from the building and carried by the water within the structure.
• Surface soiling; is caused by the accumulation of exogenic materials on the surface and it can lead to encrustation.
•Biological formations; are the growth of algae, lichen and moss on surface or plant formations whose seeds reach the structure by natural causes. Plants can cause widespread damage to masonry and roofs through their roots.
• Colour change; appears when the material is exposed to climatic factors and moist or appears due to the accumulation of unwanted materials such as salts, corrosion products or micro-organisms.
• Surface and material loss; are seen due to human-induced damages as well as the foregoing types of deterioration and factors such as disintegration, pitting, foliation that cause surface and material loss in their later stages
The conservation report includes in-situ observation, scientific data based on the laboratory analyses and intervention recommendations. In the first phase of a such study, macro-observations are made in the field to assess the conservation status of the cultural property and the mechanisms of deterioration are systematically documented while the samples are collected. When required, in-situ tests are carried out, if possible, in a non-destructive way and micro-observations are conducted via portable devices. Analyses and tests on the collected samples enable the characterization of original building materials and deterioration types. The properties of the samples are presented by physical, mechanical, and chemical tests, as well as microscopic observation and advanced analysis techniques. Either a new component or a cleaning/consolidation agent, restoration materials are characterized and the compatibility of new materials and repair methods with the authentic material is examined. The possible impact of these interventions is tested either on samples provided from the structure or in specific areas in the heritage property.
Depending on the type of deterioration, different conservation approaches can be taken, such as surface cleaning, removal of inappropriate alterations and additions, plastic repair (for material loss in stone, brick and joints), etc. Surface cleaning, plastic repair and consolidation, the most frequent actions in repair works, are guided by the analysis results and expert opinions found in the conservation report. In case of deterioration such as crust formation, soiling and colour change, the most suitable mechanical, chemical, or laser-based cleaning methods are selected in accordance with the report. In these methods, factors such as application pressure, abrasive type, solvent properties, beam wavelength and application procedure are crucial and necessary guidance is presented in the report.
