Mortars from different stratigraphic units at Portilla Castle (Alava, North Spain) have been analyzed for mineralogical characterization before radiocarbon dating. The mortar binder at Portilla Castle is composed not only of neoformation calcite but also of double-layered hydroxide (LDH) minerals such as hydrotalcite and hydrocalumite. The mineralogy of several fractions of the binder has been analyzed to determine the granulometric distribution of minerals in the binder. The continuous monitoring of mineralogy during the extraction of different grain size fractions has been performed by using a scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analyses (TGA). Hydrotalcite and hydrocalumite-bearing mortar binders give older ages than expected since they introduce dead carbon into the system.

Mortars from the cistern in Amaiur Castle (Navarre, Spain) were analysed to assess the mortar manufacturing process and application techniques. To this end, optical microscopy, scanning electron microscopy (SEM), thermogravimetric analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman microspectroscopy, and Fourier transform infrared spectroscopy (FTIR) were performed. The study of both structural and plaster mortars from Amaiur Castle cistern show patterns/rules in the mortar manufacture according to the specific construction requirements. A multilayer application technique was used for the construction of the cistern tank. Deliberate selection of the aggregate nature and grading contributed to mortar impermeability. Ceramic and silico-aluminous rock fragments were used as aggregates in the cistern tank to confer hydraulicity to the mortars, instead of carbonated aggregates as used in the vault. Aluminosilicated phases present in the aggregates led to the formation of amesite, which is a magnesium aluminosilicate hydrate (M-A-S-H) phase conferring hydraulicity to the mortar. Two types of additives were identified in the outer pigmented layer of plaster. Beeswax was the identified organic additive used to improve the impermeability of mortar, while hematite was the identified inorganic additive giving rise to the reddish colour of the layer.

This study characterises the mortar materials used in the construction of walls and floors at the Arroyo de la Dehesa de Velasco site, located near the Roman city of Uxama Argaela (the modern Burgo de Osma—Ciudad de Osma, Soria, Spain). Multilayer mortars have been characterised by petrographic, mineralogical (X-ray diffraction and scanning electron microscopy with energy dispersive analyses and geochemical analysis (X-ray fluorescence). Additionally, radiocarbon dating of the mortar binder fraction was performed in order to establish the chronology of the building in the absence of other archaeological chronological records. The results showed that similar siliceous aggregates and lime binders were used in the fabrication of multilayer system mortars. Some multilayer wall mortars show ceramic fragments or brick powder to produce hydraulic mortars and improve the resistance to moisture. The raw materials used for the construction of the site were of local origin and the construction was built during the first century BC, according to radiocarbon dating.

Archaeological lime mortars from the Tower Keep and West perimeter wall of Irulegi Castle (Navarre, Spain) were analysed to determine susceptibility to deterioration. Chemical, mineralogical, textural and physical characterisation was performed by different tests and multianalysis techniques in order to determine the intrinsic features of the original historical mortars at the castle. Samples from the Tower Keep are more prone to deteriorate compared with the West perimeter wall due to high water absorption capacity and high porosity. A high degree of pore interconnection, high desorption index and the presence of high pore volume in the 0.01 to 1 µm size range affect the mortar durability since pores retain water longer inside the mortar. Local environment conditions with persistent annual rainfall, high humidity and temperature variations contribute to the decay process of the original mortar. Characterisation of historical mortars not only allows better understanding of susceptibility to deterioration but also helps the design of compatible and durable repair mortar for future interventions on historical heritage. Compatibility of new materials with the historical mortar will be ensured by studying mortar characteristics and properties.

Historical lime mortars provide valuable information on the construction phases of buildings and allow reconstruction of the chronology of the historical structures. The City Wall of Burgos and the Mudejar Arch of San Martin were declared an Asset of Cultural Interest and have been protected since 1949. Several restorations at the end of the 20th century altered the original appearance of the wall and the current gate, making it difficult to establish stratigraphic relationships between the two structures. Given the scarcity of information on the construction phases of the wall and the uncertainty of the historical dates, a mineralogical and chemical characterization of the mortars was carried out, and the suitability of the binder for radiocarbon dating was assessed. The petrographic, mineralogical and chemical analyses of the lime mortars from the Arc of San Matin show distinctive characteristics, suggesting different construction periods and production processes, where the selection of raw materials and production methods was conducted according to the construction requirements. Moreover, the presence of contaminant phases and microparticles of charcoal in the binder fraction led to discard all the samples for mortar radiocarbon dating.

Historical information about the chronology of Burgos’s medieval wall has never been ratified by urban archaeology in the city, while its construction was neither linear nor took place at a single time. This article presents the archaeological study carried out at the gates of San Juan and San Martín, the entrance and exit of the French Way of St James in the medieval city. The funerary use of the former came to an end in the late Middle Ages, when a section of the wall was built. At the latter, at least three building phases are known and supported by the stratigraphic sequence, the mineralogical comparison of the mortars and a 14C AMS date. Profound renovation of the urban plan in the fourteenth century has been demonstrated at both sites.