Degradation of ancient Maya carved tuff stone at Copan and its bacterial bioconservation Elert, Kerstin Ruiz Agudo, Encarnación Jroundi, Fadwa González Muñoz, María Teresa Rodríguez Navarro, Carlos Manuel We acknowledge funding by the Santander Program for the Research and Conservation of Maya Sculpture, at the David Rockefeller Center for Latin American Studies (DRCLAS), Harvard University; the Spanish Government grant RTI2018-099565-B-I00, the Junta de Andalucia research groups RNM-179 and BIO 103, and the University of Granada, Unidad Cientifica de Excelencia UCE-PP2016-05. We thank the Instituto Hondureno de Antropologia e Historia (IHAH) and the local Santander team at the Maya Sculpture Conservation Laboratory (LACEM) in Copan including Hector Eliud Guerra, Karina Garcia, Adelso Canan, Rufino Membreno, Luis Reina, and Isuara Nereyda Alonso for their help and continuous support, as well as for providing access to this Maya archaeological site and their contribution to the documentation, sampling, and treatment application process. We also thank architectural conservator Laura Lacombe for sampling support, Fulvio di Lorenzo for his help with Rietveld analysis of XRD results, George W. Scherer for his insightful comments on clay swelling damage, and the personnel of the Centro de Instrumentacion Cientifica (CIC) of the University of Granada for their help with TG/DSC, XRD, FRX, mu-CT, FESEM and TEM analyses. We also thank Aurelia Ibanez Velasco for her help with the expansion tests, as well as with the porosity and water absorption analyses, and Jean Battini from Micromeritics France S.A.R.L., for the MIP analyses. Much stone sculptural and architectural heritage is crumbling, especially in intense tropical environments. This is exemplified by significant losses on carvings made of tuff stone at the Classic Maya site of Copan. Here we demonstrate that Copan stone primarily decays due to stress generated by humidity-related clay swelling resulting in spalling and material loss, a damaging process that appears to be facilitated by the microbial bioweathering of the tuff stone minerals (particularly feldspars). Such a weathering process is not prevented by traditional polymer- and alkoxysilane-based consolidants applied in the past. As an alternative to such unsuccessful conservation treatments, we prove the effectiveness of a bioconservation treatment based on the application of a sterile nutritional solution that selectively activates the stone ' s indigenous bacteria able to produce CaCO3 biocement. The treatment generates a bond with the original matrix to significantly strengthen areas of loss, while unexpectedly, bacterial exopolymeric substances (EPS) impart hydrophobicity and reduce clay swelling. This environmentally-friendly bioconservation treatment is able to effectively and safely preserve fragile stones in tropical conditions, opening the possibility for its widespread application in the Maya area, and elsewhere. 2021-10-13T07:50:11Z 2021-10-13T07:50:11Z 2021-08-17 info:eu-repo/semantics/article Elert, K., Ruiz-Agudo, E., Jroundi, F. et al. Degradation of ancient Maya carved tuff stone at Copan and its bacterial bioconservation. npj Mater Degrad 5, 44 (2021). [https://doi.org/10.1038/s41529-021-00191-4] http://hdl.handle.net/10481/70816 10.1038/s41529-021-00191-4 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Springer