Prevention of Salt Damage to Monuments: Esem and Time-Lapse Studies

Abstract Introduction: “In time, and with water, everything changes.” —Leonardo da Vinci The crystallization of soluble salts in porous building materials is a widespread weathering process that results in damage to important monuments and archaeological sites. Salt weathering by thenardite (sodium sulfate) and mirabilite (sodium sulfate decahydrate) is especially destructive, yet is still not fully understood. Halite (sodium chloride) in contrast, is one of the least damaging salts. Previous work has also demonstrated the importance of airflow in salt weathering. Here we present new data that help explain why sodium sulfate is so damaging and also show how crystallization modifiers and changes in airflow can reduce salt damage in laboratory experiments. Damage Mechanism: The behavior of sodium sulfate was documented using saturated solutions and oolites from Monks Park limestone (a stone well known to be vulnerable to salt damage) as test samples. Damage was evaluated based on the degree of cracking of the oolite.