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Carbonate materials – limestone and lime stuccos – were widely used in ancient Maya construction. Deterioration of these materials presents a major problem for the conservation of Maya architectural heritage. However, the mechanisms of deterioration and their interaction with the diverse inner structures of these materials are still insufficiently understood. We performed micromorphological and mineralogical research of the limestone alteration in the buildings of Rio Bec and stuccos in Dzibanche, two Late Classic Maya sites in the southern Yucatan peninsula. Dissolution and recrystallization of calcite were found to be universal and the most important weathering process in both materials. Dissolution is selective, affecting mostly micrite. Larger crystals, especially rhombohedral calcitic pseudomorphs developed after dolomite, are more stable. Selective dissolution of micritic cement of limestones and stuccoes enhances physical breakdown by producing numerous pores and loosening bounds between coarser inclusions. This process clearly controls the deterioration grade of different limestones: those with more intensive fragmentation and powdering have higher contents of micrite. Secondary carbonates are represented mostly by acicular calcite filling fissures and forming coatings on the outer surface. Clear spatial relation to fungi and roots and their similarity to well-known soil neoformations indicate biogenic origin of these neoformations. In most cases, they contribute to macroscopic powdering being loose. However, in the cracks of some limestones they form dense infillings, which could plug the fractures and prevent further advance of weathering to the core of the stone. Neoformed sulfates and iron oxides are fewer, but also participate in the deterioration.

[EN] Researchers have related the manufacturing technique of plasters and stucco in the Maya area with their period of production but not with their architectural function. In this paper, we establish a relationship between those three features (manufacturing technique, age, and architectural function) in the plasters of the Maya site of Dzibanche in southern Quintana Roo. Dzibanche has abundant remains of stuccos and plasters found mainly in three buildings (Plaza Pom, Pequena Acropolis, and Structure 2). We used thin sections, SEM and XRD, and archaeomagnetic dating processes. The pictorial layer of Structure 2 was the earliest (AD 274-316 and the stuccoes and plasters of the other two buildings were dated to the Middle Classic (AD 422-531), but we obtained different archaeomagnetic dates for the red pigment layers found in the buildings of the Pequena Acropolis and thus we were able to determine their chronological order of construction. The raw materials and proportions were carefully chosen to fulfil the mechanical necessities of the architectonic function: different proportions were found in plasters of floors, in the external walls, and inside the buildings; differences between earlier and later plasters were also detected., We acknowledge the archeological project of Dzibanche and Centro INAH Quintana Roo who generously allowed the extraction of the samples for this study; also we acknowledge the Universidad Nacional Autonoma de Mexico that gave a grant that allowed a three month research in the laboratories of the Universitat Politecnica de Valencia. Financial support for the analysis of organic materials is kindly acknowledged; it was provided by the Spanish MINECO R+D project CTQ2014-53736-C3-1-P and also supported with ERDEF funds. The authors thank Jaime Diaz for his assistance in preparing thin sections.