Study of the influence of limewash on the conservation of Islamic plasterworks through weathering tests

Abstract

In a previous study, a layer of limewash was detected over the gypsum plasterworks used to decorate different spaces of the Real Alcázar of Seville such as interior rooms, patios and outdoor galleries. In this paper its use is analysed, namely whether it improves the properties of the plasterworks and provides a protective effect, through accelerated weathering tests designed specifically to reproduce real environmental conditions. Plaster specimens with similar composition and physical characteristics to those of the original plasterworks were prepared. After the cure of the specimens, the application of a layer of limewash was made. Samples were subjected to weathering tests that consist of water absorption cycles (by capillarity and immersion) and drying.

The results showed that the application of limewash did not improve the durability of the plaster significantly, although seemed to have a more protective effect against weathering by capillarity tests in the specimens prepared with a higher water/plaster ratio. In fact, after the immersion tests a great part of the limewash layer became detached, while in the plasterworks of the Real Alcázar this behaviour has not been observed. So, capillarity tests seem to be more adequate to reproduce the real weathering conditions of these ornamental elements.