2023 Theses Master's

Salt Crystallization Inhibitors: An analysis of compounds, application methods, and testing techniques

Leach, Michelle

Salt damage has long been listed as a major cause of deterioration for porous building materials, but the conservator’s toolbox is surprisingly light when it comes to treatments. Salt crystallization inhibitors (SCIs) emerged over the last twenty years as a possible treatment to prevent damage. This research focused on the evaluation of diethylenetriamine penta (methylene phosphonic acid)—also called DTPMP—and potassium ferrocyanide for preventing sodium sulfate damage to Indiana limestone and Berea sandstone. Samples were treated in the laboratory using a range of application methods and were exposed to aqueous sodium sulfate. Multiple experiments were conducted to understand the success of inhibitors to modify efflorescence, to evaluate the application methods, and to understand the interaction between these inhibitors and the desalination properties of traditional poultice materials.

Poultice application showed the most promise for applying SCIs, with samples from this treatment group displaying the most consistent change from control samples. A longer dwell time proved successful for treating the sandstone samples; capillary uptake treatments were hindered by bedding planes. Upon application using a poultice, it became clear that the use of ferrocyanides should be limited to stones with minimal-to-low iron contents due to a bluing reaction. DTPMP was successful in changing crystallization patterns in Berea sandstone, but its ability to prevent damage proved more complicated. Using inhibitors as additives in desalination poultices did not provide more efficient salt extraction and using an inhibitor prior to a desalination poultice can decrease salt extraction in some stone types.