Geopolymers in cultural heritage: their application in azulejo conservation

Abstract

Currently, the restoration materials used to fill gaps in architectural historic azulejos (e.g. lime or organic resin pastes) present relevant drawbacks in terms of compatibility, efficacy or durability. The current solutions are not able to fully protect the azulejos resulting in further deterioration. Geopolymers can be a potential solution for azulejo lacunae infill given the chemical-mineralogical similitude, durability and versatile range of physical properties that may be obtained through the manipulation of their formulation and curing conditions. This communication presents and discusses the viability of the use of geopolymeric pastes to fill lacunae in azulejos or to act as “cold” cast ceramic tile surrogates reproducing missing azulejo fragments. The formulation of geopolymers (type and concentration of activators, aluminosilicate source and water content) and curing conditions was optimized. The need for post-curing treatments (desalination) was also taken into consideration in view of the purpose of their application: the restoration of outdoor architectural historic azulejos, which are exposed to adverse environmental conditions. The possible advantages and disadvantages of the use of geopolymers in the conservation of azulejos is also discussed.