Lime, considered as an historical construction material with its earliest documented use from the IV millennium BCE, in Egypt, is the basis for most Roman mortars. It was used as a binder for different types of aggregates, being sand the most common one. Lime mortars could have different functions in a construction, from a block binding element to a wall covering material or a pavement levelling layer. In the case of the latter, one of lime’s applications was in the construction of mosaics, namely in the production of each of its strata of lime-based mortars. These included the lit-de-pôse, a layer of high lime/sand ratio mortar with very fine particle size distribution, on top of which, each tessella was immobilised, to form the decorative motif.

At the archaeological site of Conimbriga, holder of an extensive collection of Roman mosaics, the remains of what was originally Roman lime from the Ist c. CE, in the shape of a block, were found in a dolium, a large ceramic container, what seems to point to a traditional way of production. In order to study the relation between the original raw material and its possible application in Conimbriga’s mosaics, samples of this material were characterised by means of X ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and gas picnometry (GP).

First results on the characterisation of the lime point to the existence of calcite, quartz and magnesium hydroxide indicating the use of Mg-rich or even dolomitic limestone in its original production. This study will contribute to the clarification and assessment of the historical materials used in the construction of Roman mosaics from Conimbriga in Portugal.

Abstract presented in the Conference Materiais 2019, 14-17 Abril 2019, Lisboa, Portugal