Researchers in the Framework Programme 6 project SALTCONTROL have developed a crystallization inhibitor that prevents the growth of salt crystals within the pores of stone. The process has been tested on two of Europe’s most significant heritage buildings.
Humidity, environmental pollution and cleaning products can all prompt the formation of salt crystals in stone, leading to a gradual process of decomposition and causing paint to flake.
Existing treatments are cosmetic, and until now it has been assumed that salt damage was an unavoidable consequence of ageing. Researchers in the SALTCONTROL project set out to develop a technique to block the mineral salt crystallisation process inside the stone.
Scientists at the University of Granada tested possible treatments on rock extracted from the Santa Pudia quarries in Escúzar, Granada. Stone from this quarry was used in the construction of many of Granada’s famous Renaissance buildings, such as the Monastery of San Jerónimo, the Cathedral and the Royal Chapel. These buildings are very prone to damage due to crystallisation of sodium sulphate, magnesium and sodium nitrate.
There followed a series of laboratory tests, and in the final phase of the project, the crystallisation inhibitor was tested in pilot areas of the Monastery of San Jerónimo.
The SALTCONTROL researchers have developed a methodology for studying crystallisation in individual buildings, carrying out laboratory tests to select the concentration, pH and most appropriate way of applying the inhibitor, and going back to the building to test discrete areas, before applying treatments over wider areas.
SALTCONTROL ran from 2004-2007. Apart from Granada, it involved researchers from the universities of Münster, Germany, Ghent, Belgium, University College London, UK, Patras, Greece, the Technical University of Prague, the Architecture Conservation Centre TNO of Holland, the Andalusian Institute of National Heritage and the Technical University of Eindhoven.
Apart from the Monastery of San Jerónimo, the crystallisation inhibitors developed by the project have been successfully applied to the Fortress of Teresina in Prague.