Salt degradation of historic portuguese azulejos

Abstract

Research was carried out to study the degradation of the glaze layer of a set of Portuguese tiles from the 17th and 18th centuries. The ageing action of NaCl salt has been tested on a group of tiles that presented different characteristics and defects on their glaze layer. The defects resulted from previous degradation or manufacturing faults. The research results show that tile characteristics such as the porosity, vapor permeability, drying rate and especially the occurrence of some particular glaze defects were the most dangerous decay drivers.