Intemperismo tropical em fachadas azulejadas de edificacoes historicas em belem do para

Abstract

The application of European tiles on building façades of Belém city started since 19th century. After hundred years under weathering action, the tiles started to show alterations. To understand these weathering action two historical buildings of the 19th century were studied: Palacete Pinho and Solar do Barão de Guajará, located on Belém old town. The Palacete building has German tiles (PPA and PPA-C) and Portuguese tiles from Porto city (PPP). The Solar building has only Portuguese tiles on its main façade, from Porto city (BGFP). Dark stains are the main kind of alteration found in the German tiles. They are located between the glaze and the ceramic part, without lost of glaze. In case of the Portuguese tiles from both buildings, the lost of glaze is frequent, besides the presence of green stains under the detached glaze. Physical characterization results are as follow: 1) the German tiles (PPA and PPA-C) have a lower accessible porosity (12.96% and 9.59%, respectively) and higher density (1.99 g/cm3 and 1.92g/cm3, respectively), than the Portuguese ones (PPP: 29.34% and 1.59 g/cm3 and BGFP: 17.53% and 1.74 g/cm3); 2) the Portuguese tiles present glaze thickness between 0.06-0.1 mm (PPP) and 0.5-0.54 (BGFP) and the German ones between 0.04-0.2 mm (PPA and PPA-C); 3) Portuguese glazes exhibit an abrupt contact with the ceramic part while German tiles show a transition zone between these two layers. Mineralogical analyses of the ceramic parts were carried out using XRD and SEM/EDS. The main mineral phases identified are: quartz, mullite, and cristobalite (German tiles) and quartz, gehlenite, diopside and calcite (Portuguese tiles). Quartz, cassiterite and apatite were also found in both German and Portuguese glazes; only the PPP sample does not have cassiterite. Total chemical analyses of the ceramic parts of German tiles indicated a major amount of SiO2 (75%) and Al2O3 (18%). In the Portuguese tiles, besides SiO2 (46%) and Al2O3 (15%), there is also high CaO contents (22%). Concerning the glazes, the chemical composition is mainly composed by Si and Pb. The green and dark stains beneath the glaze are related to microorganisms of the Cyanophyta and Bacillariophyta divisions. Climatic data records from Belém city were recovered since 1898 and showed that no significant climate changes happened in the region. Rain water sampling and analysis were also carried out in the vicinities of the two studied buildings. 11 The results show small Ca concentrations above regular levels for rain water, which can be related to the mortars. The temperature measurements on tile surfaces indicate variations for different parts of the façades. In the Solar Building, areas of high surface temperature are those where the glaze was unattached to the ceramic bodies. The results showed that the tiles are rather resistance to the tropical weathering. German tiles have a minor glaze lost because of the interface zone between glaze and ceramic part. The absence of such zone in the Portuguese tiles turn then more prone to weathering due to climate changes, mainly thermal daily variations, which lead to glaze detachment.