Investigation on 19th century fired bricks and lime plaster for the conservation of historical building materials: a case study of the Church of Sant Rafael (Barcelona, Spain)

Abstract

This paper studies the fired bricks and plaster from the Church of Sant Rafael (Barcelona) in a multi-analytical approach based on mineralogical, chemical and physical characterization. The different analyses provide valuable data on the raw materials and production technologies involved in the manufacture of the studied 19th-century materials. The results suggest that a multi-layer preparation technique was used to apply the plaster, with a marmorino as the final outer layer. The identification of diopside and åkermanite neoformed magnesium phases suggests that Mg-carbonate rich clays were used for the production of bricks. The presence of hematite and the new high temperature phases, diopside, åkermanite and anorthite, suggest that the raw clays were fired under oxidising conditions at temperatures of ca. 900–1000ºC. The high volume of micropores smaller than 2 µm and the high and fast water absorption capacity of the brick placed under a tiled floor are the main factors contributing to rising damp, favouring a progressive deterioration process. Moreover, gypsum was identified as the weathering product affecting the conservation of the church.