Characterisation of Roman coatings from the a Roman house in Mérida (Spain)

Abstract

This work focused in the study of mortars from the Mithraeum house (Mérida, Spain). Fifteen samples of lime-based Roman coatings mortars of the house of Mithraeum were analysed. Samples can be divided into five main groups: hydraulic mortars, plaster mortars, coating mortars, stuccos and intervention mortars. The apparent bulk density, porosity, adherence, pH chemical composition and particle size of aggregates were measured according to the standard rules. The hydraulicity and the cementation indexes were calculated. X-ray diffraction analysis of finely pulverised samples, optical microscopy with transmitted and polarised light and scanning electron microscopy (SEM) with energy dispersive analyses (EDX) techniques were used to examine the morphology, microstructure, and the texture of the mortars. The wall covering of Mithreum house was made with thick layers of lime mortar and coloured stuccos. Plaster mortars compositions were in the range 1/2.5/0.1 and 1/4.1/0.2 (lime/sand/arid), and, as usual in Roman mortars, do not contain gypsum. In these mortars, a calcareous lime was used (not dolomite). The sand used in each layer of the columns of viridarium is different. In the microphotographs the great homogeneity achieved in the mixtures are shown. The technique of mixture of arid and lime was perfect in both kind of mortars. A great portion of these ceramic pieces mixed with mortar were found in walls of the ponds, canals and, tanks. It can be concluded that in the whole Roman Empire a wide knowledge of the mortars and very strict standards existed. They use high purity lime, and aggregate siliceous sand, marble dust and crushed ceramic. The durability of these coating mortars gives an idea of the knowledge Roman technicians had in manufacturing and applying mortars. It has to be noticed that it is within the limits set in the current regulations concerning aggregates of mortars that gives information about the quality level of these Roman mortars. This information can be very suitable for both intervention and restorations of archaeological remains and to incorporate them into new buildings and existing buildings.