Characterization of archaeological mortars from Herculaneum

• Mortars from various types of floors at Herculaneum were sampled.
• Mortars were analyzed by XRF, Petrographic analysis and TGA/DTG.
• Foot traffic of visitors seems to induce decay on mortar-based floors.
• Samples collected from floors placed under faulty shelters showed sulphurous compounds.
• Samples deriving from bath complexes showed the Chlorine compounds.

This paper concerns the characterization of mortars sampled from various types of floors at the archaeological site of Herculaneum, Italy in 2010–2012. Sampling was carried out within a project (“100 Mortars Project”) that aimed to study the wide range of mortars present in the archaeological site to increase knowledge of the use of ancient mortars at Herculaneum in wall fabric and in decorative features, achieve a better understanding of decay, improve choices in the preparation of new mortars which are as compatible as possible with the existing.Despite the archaeological and historical importance of Herculaneum, far fewer scientific studies on Roman materials and techniques have been carried out at this site than at Pompei. Thirty-three samples of mortar were taken from different kinds of floors, i.e. opus signinum or “cocciopesto” (ground brick dust and slaked lime) with or without insertion of marble chips, bedding mortars of mosaic and opus sectile across the entire archaeological site. Mortars were analyzed by Elemental (XRF), Petrographic (PA) and Thermal Analysis (TGA/DTG). Thermal Analysis results subjected to multivariate analysis (cluster analysis) allowed to group samples on the basis of the formation of degradation compounds which altered the thermal parameters and correlated them to conservation conditions.