Studies on original mortars can greatly assist archaeological interpretations, as elucidating the composition of such mortars gives clues on the origin of raw materials, manufacturing technology, and the construction phases of a site. This article presents the multi-analytical characterisation of 24 mortars and plasters from the Żejtun Roman Villa, Malta, to support archaeological hypotheses on the history of the construction of the site. The samples, belonging to at least three distinct phases included in the stratigraphy of the Żejtun archaeological site, were analysed using polarised light microscopy (PLM), scanning electron microscopy (SEM–EDS), X-ray diffraction (XRD), thermogravimetry (TGA/DSC), X-ray fluorescence (XRF), ion chromatography (IC), and stable isotope analysis (¹³C and ¹⁸O). The assessment of the results through correlations with archaeological evidence identifies five types of mortars with varying degrees of hydraulicity. These are associated with different development phases of the site and distinctive uses and were mainly produced using local resources, except in the Early Roman period when natural pozzolanic raw materials started being used. As there are no natural pozzolans on the Maltese Islands, it is hypothesised that the pozzolanic materials used as aggregate in the mortars were imported to the Islands from neighbouring volcanic regions. This volcanic aggregate was especially abundant in one of the mortar types, which was used mainly as a bedding mortar for floors.

Petrographic and petrophysical characterization of aerial and hydraulic mortars allows their differentiation and the establishment of their most suitable applications. Natural, aerial or hydraulic lime mortars as well as artificial cements mortars present different physical properties. It shall be noted that physical characteristics, which depend on petrographic characteristics, impact on its mechanical properties. Therefore, this comparative study with standardised techniques and tests, has analysed these mortars from a petrographic, petrophysical and mechanical point of view. The chemical processes and porosity originated during mortar production and subsequent curing phase explain mortar physical behaviour (hardness, strength, as well as fluid access and retention). This study confirms that air lime mortars are the most porous and least resistant while cement mortars are the most resistant and impermeable. Finally, natural hydraulic lime mortars, with petrographic characteristics similar to cement mortars, have physical-mechanical properties close to aerial ones, although they are more impermeable and resistant.

Building materials used at the Former Workers Hospital of Maudes, Madrid (Spain) were studied. The study addressed the information both achieved from documental resources and characterization techniques. Documentary work has enabled to know about the architect thought, the ideology of the project or the grounds that conditioned such materials selection; it also permitted to learn about materials provenance and/or its elaboration. Analytical studies provided information about petrographic features of the materials and their composition; limestone provenance was confirmed and new data on material manufacture were provided. Such information, which deserves to be known and disseminated, provides a significant heritage value to materials that shape cultural assets. Studies with a multidisciplinary approach represent a commitment to improve the knowledge and conservation of heritage.

Sandstones have been widely used in construction for their abundance, aesthetics, and ease of extraction. To determine sandstones’ quality, it is essential to analyse their petrographic and petrophysical properties and sensitivity (durability and conservation) to environmental agents. This paper evaluates the physical-mechanical changes undergone by Sierra de la Demanda (Burgos, Spain) sandstone under combined and induced water and salt aggression and assesses ESTEL 1100’s effectiveness and suitability as a treatment. This sandstone is porous, permeable, dense and quartz-rich with high hardness and strength. The treatment improved its petrophysical properties by modifying its pore geometry and connectivity, reducing absorbency, permeability and anisotropy, and further increasing its hardness and resistance. Salts did not substantially modify its properties as its porosity type absorbed the crystallisation pressure. Ultimately, its pore system and predominantly quartz composition make it a high-quality, weather-resistant material compatible with the treatment applied.