An Investigation of Suspected Salt Crystallization Deterioration of Fine-Grained Limestone Used as Architectural Cladding

Where once architectural stone was primarily locally sourced, the modern global economy gives designers and brokers access to exotic stones worldwide. It is widely understood that stone performance can be variable in differing climates, and whether the initial stone selection is made purely for aesthetics or considers physical properties, the natural heterogeneity of stone can result in undesirable issues for appearance or structural performance of the material. When stone cladding performs unexpectedly, an investigation is necessary to diagnose the underlying issues. A fine-grained limestone is installed at a private residence on the Gulf Coast. Quarried in Turkey and fabricated in China, within weeks of installation, the stone exhibits persistent efflorescence and spalling. Subsequent shipments arrive with surface encrustations and scaling. Salt contamination during fabrication or shipping is assumed, but is the minerology of the stone contributing? Can the long-term durability of the stone under the predelivery salt contamination be predicted? Is the deterioration exacerbated by in situ exposure to a marine environment? Preliminary petrography of the limestone identifies calcite and sodium sulphate-phase minerals, along with halite and trace clays. A testing protocol is developed to identify both contaminating and inherent salts, including a salt crystallization durability test. There is currently no ASTM standard for this property, although standard development is in process. Using EN 12370 as a starting point, performance of the Turkish limestone under cyclical salt crystallization is explored. This paper reviews the advantages and limitations of EN 12370, including the results of modifications made in an effort to replicate real-world salt exposures to compare against the baseline but aggressive conditions of the EN test method. The results of this investigation will provide supporting data to C18 and the broader practice on the application of EN 12370 when considering long-term performance of stone under salt contamination.