Investigation of the deterioration mechanisms induced by moisture and soluble salts in the necropolis of Porta Nocera, Pompeii (Italy)

Abstract

AbstractThis paper focuses on the diagnosis of damage processes of decorative Roman renders of a group of tombs in the Porta Nocera necropolis in the ancient city of Pompeii, Italy. Unprotected from various climatic events, the tombs keep on deteriorating since they were first excavated in 1954. Extensive on-site and laboratory diagnostics using non-destructive and low-destructive techniques have been able to demonstrate that soluble salts are among the major agents of deterioration, causing damage in the form of render delamination. Gypsum is formed on the surface of the materials by the deposition of sulfur dioxide, resulting in reduced porosity and hardening of the surface. Soluble salts of nitrates and chlorides that penetrate the tombs’ masonry from the ground and are transported through the render layers tend to crystallize in subsurface. The crystallization—dilution cycles of the soluble salts cause major mechanical pressures, leading to the progressive destruction of the renders. Past conservation strategies to secure plasters have shown only limited effectiveness. In light of the data collected regarding salt decay, the authors propose new strategies, questioning the systematic use of grouts and restoration mortars for conservation treatments and focusing on preventive conservation and maintenance to ensure the long-term preservation of masonry and decorative surfaces of the tombs.