Technological properties and conservation problems of some medieval bricks and tiles

Dinçer, Ayşe Şenay
The aim of this study is to examine the technology of the relatively deteriorated historic tile, brick and mortar samples of Sivas Gök Medrese and Tokat Gök Medrese. Their main deterioration factors were analyzed mainly as salt weathering. It was examined in detail, and the possible desalination methods were discussed. For this purpose, the studies were carried out with a field survey and laboratory experiments on the two sites. Documentation of visual decay forms of Tokat Gök Medrese were done with AutoCAD. The density and porosities of tile body and mortar samples were determined by using RILEM standards. The pore size distributions of tile and mortar samples were examined by Mercury Intrusion Porosimetry. Modulus of elasticity of tile body and mortar samples was determined and compared with the other Seljuk building materials. Mineralogical compositions of the tile body and glaze, adhesive tile mortars of Sivas Gökmedrese and Tokat Gökmedrese were analyzed with X-Ray Powder Diffraction (XRD). Their microstructure and chemical compositions were determined by using Scanning Electron Microscope coupled with Energy Dispersive X-Ray Spectroscopy (SEM-EDX). The salts were determined for various methods such as spot tests and XRD analyses. The possible treatment methods of salt crystallization were discussed according to the properties of the examined samples. One of the most essential causes of decay factor was salt crystallization for the two buildings which causes detachment and loss of tiles. The deteriorations were distributed over the upper and lower sides of the wall which were close to the dampness zones from the roof and above ground. The experiments proved different kinds of salts such as thenardite, sylvite, halite, natrite, nitratine and niter coming from the ground and the restoration materials such as cement based mortars. The relative humidity of the environments was compared with that of salt characteristics. It was proved that the tiles were adversely affected from salt crystallization. The best desalination method was discussed. Advection method by using poultices was based on the transformation of ions through the flowing moisture. The most prominent characteristic of the poultices must have smaller pore size distribution than original salty materials. The pore size distributions of the tiles and gypsum mortars were determined to compare and chosen the best poultice from the literature. It was concluded that kaolin-sand-based poultices having known properties was the best one as considering the pore size distribution of the tiles and mortars. The study on material properties and desalination process was expected to help different monuments having salt problem.