Performance-Based Evaluation of Salt Crystallization Inhibitors as a Means to Mitigate Salt Damage in Terracotta

The impetus for this research was the need for a conservation treatment of salt-laden terracotta inside kiln #8 at Western Clay Manufacturing Co.- a historic brickyard in Helena, Montana. Western Clay stands as an example of how traditional methods of mitigating salt damage, like water-immersion and poulticing, are not possible or effective in certain circumstances. Therefore, the focus of this study was to investigate salt crystallization inhibitors as an alternative method to mitigate salt damage in terracotta. Salt damage is one of the most common mechanisms of deterioration in building materials, which makes the results of this research widely applicable. A performance based evaluation of salt crystallization inhibitors was conducted, using sodium and potassium ferrocyanide, each with and without the addition of sodium hexametaphosphate. These chemical reagents were applied to terracotta samples contaminated with sodium chloride, sodium sulfate, and an equal mixture of the two. It was found that there was no measurable change in the sodium sulfate contaminated samples. It was found that all inhibitors had the ability to increase supersaturation, delay nucleation, and effectively changed the morphology of salt crystallization of sodium chloride, which was evident through the dramatic increase in efflorescence and a reduction of material loss that was observed in the sodium chloride and sodium chloride/sodium sulfate contaminated samples. It was found that potassium ferrocyanide and potassium ferrocyanide with sodium hexametaphosphate had the greatest effect. The positive results of this research warrants further testing and analysis, as salt crystallization inhibitors show promise of being a conservation treatment of the future.