The conservation works for volcanic tuffs used in Ahi Celebi Mosque

Tarihi yapılarda sıkça kullanılan ve hızlı bir şekilde hasara uğrayan ve Osmanlı arşiv belgelerinde 'od taşı' olarak adlandırılan yeşilimsi renkte volkanik tüfler üzerinde bir koruma-onarım (konservasyon) çalışması yapılmıştır. Çalışma yöntemi iki aşamalıdır. Birinci aşamada konuyla ilgili literatür çalışması, ikinci aşamada ise, deneysel çalışmalar yer almaktadır. Deneyler, önceden seçilen tarihi yapıdan alınan taş örnekleri üzerinde yapılmıştır. Bu deneysel çalışmalar üç adımda toplanmaktadır. Bunlar; 1. Özgün taşın bozulma morfolojisinin ve sağlam kısmının özelliklerinin belirlenmesi, 2. Sağlamlaştırıcı-koruyucu kimyasallarla yapılan iyileştirme çalışmaları, 3.Kimyasalların etkinliğinin değerlendirilmesidir. Özgün taşın bozulma morfolojisi ile sağlam karakterinin belirlenmesi için fiziksel, kimyasal, mekanik özellik deneyleri ile mikro yapı analizleri paralel olarak yapılmış, sonuçları karşılaştırılmıştır. Daha sonra aynı örneklere, etil silikat cinsi sağlamlaştırıcı ve silan-siloksan esaslı su itici kimyasallar fırça ve daldırma yöntemi ile uygulanmıştır. Polimerizasyon süresi için 4 hafta bekletilen örneklerde daha önce yapılan benzer deneyler tekrarlanarak sonuçları karşılaştırılmıştır. Son olarak, kimyasalların etkinliğini değerlendirmek için ıslanma-kuruma ve donma-çözülme çevrimleri ile tuz kristallenmelerine dayanıklılık deneyleri yapılmıştır. Sonuçta, yapıdan alınan volkanik tüf örneklerinin riyodasitik-dasitik tüfler olduğu, hava kirliliği ve atmosferik olaylar sonucunda fiziko-kimyasal bir bozulmaya uğradığı belirlenmiştir. Bozulan taşların, silan/siloksan esaslı sağlamlaştırıcı ve su itici kimyasalların uygulanması ile su emme oranlarının % 90 azaldığı, ultrases hızlarının da yaklaşık % 30 arttığı bulunmuştur. Ayrıca, kimyasal sürülen örneklerin, yapılan üç farklı eskitme deneylerinden kimyasal sürülmeyen örneklere göre daha az etkilendikleri görülmüştür. Anahtar Kelimeler: Volkanik tüf, bozulma morfolojisi, konservasyon çalışması, su iticiler.In this study, a conservation method was studied for green coloured volcanic tuffs called 'od stone' in Ottoman archives documents. These stones were commonly used in Early Byzantine and Late Ottoman Buildings in the walls, window frames and stairs, etc. These have a fire resistance against the high temperatures so it was called od stone. And they were quarried from Yalova-Karamürsel region in Turkey. The volcanic tuffs which are rather frequently used in historical buildings and monuments are deteriorated by various effects because of their chaotic micro structure. Also, there is less study in the world wide literature about the conservation of volcanic tuffs. By means of this study, a method will be recommended to obtain a common language between the specialists who take part in the interdisciplineary team work of conservation and restoration of historical buildings. The constituting a methodology of conservation and restoration are also applicable on other types of stones. The research was studied in 2 steps. In the first step, a widely literature research related to the subject and in the second step, laboratory tests following the suggested conservation method in the study were carried out. Tests were conducted on original stones which were sampled from the Ahi Celebi Mosque, which is located in Eminönü. It was built in 16th century by Architect Sinan. One of its facades is near to sea (Golden Horn) and the other facades are near to traffic. And it has also ground problems. This building was highly affected by the salts coming from the sea and the air pollution caused by traffic. Especially, the od stones used in the walls and window frames were seriously deteriorated. For that reason, od stones were sampled from this building for the conservation study. Planned laboratory tests that are required for the conservation study consisted of 3 steps: 1. Step: Determination of deterioration morphology and sound core of original stone; This step consisted of macro and micro analyses conducted on the original od stone samples such as physical, mechanical property tests and chemical and petrographical analyses. These tests and analyses were conducted on sound core and deteriorated surface of the sample. As a result of these tests, od stones were found as a rhyodasitic-dasitic tuff because of having quartz, plagioclase, alkali feldspar, zeolite etc. silicate minerals. And deterioration morphology was determined by finding 'montmorillonite' as a clay mineral in the micro structure. This was found in the result of the conversion of feldspar minerals in to clay minerals by the cause of the air pollution and atmospheric events. 2.Step: Consolidation and preservation applications with chemicals; Conservation works were carried out on the od stones taken from the mosque. Stone conservation works were performed by applying the chemicals which have consolidant and protective properties on to the deteriorated stones with some alternatively changed consolidation and protection methods. During the processes, impregnation depth and penetration depth tests were conducted on the samples. As a consolidating agent, ethyl silicate (undiluted), and as a water repellent agent siloxane (1:11 diluted by white spirit) was used by brush and immersion method for the od stone samples. After curing of 4 weeks for polymerization, the efficiency of chemicals was examined by aforementioned tests. 3.Step: Evaluation of the durability performances of chemicals; The evaluation of the effectiveness of the chemicals was carried out as to the results of the artificial weathering tests applied on the treated and untreated samples of original stones. In this step, some weathering tests such as, durability for salt crystallisation, wetting-drying and freezing-thawing cycles were conducted. After these aging tests, physical, mechanical property tests on the stones were repeated and these results were compared with the previous test results in order to evaluate the developments of the treated samples. In the conclusion, it was found that by using consolidant and water repellent, the water absorption value of the od stones was decreased 90% and ultrasound velocity value was increased 30% after treatment. At the end of all these tests, ethyl silicate and silane/siloxane were suggested as a consolidant and water repellent pair from those tested chemicals. This method can be applied for the other type volcanic tuffs which consist of silicate minerals and which have surface erosions, stone replacement is recommended for deep alterations. Keywords: Volcanic tuff, deterioration morphology, conservation methodology, water repellents.