Active conservation of ceramic building materials: removal of lichens on roof tiles by laser and biocides treatments

Esta comunicación participó en el: 5th International Conference YOuth in COnservation of CUltural Heritage YOCOCU 2016 21st-23rd September 2016 MadridVery recently, in monumental cities, certain conservational practices tend to use ancient/traditional roof tiles in the restoration of Heritage buildings. Numerous studies have been undertaken to remove lichens on stones. However, little has been done to date to study lichens removal from ceramic materials, despite the fact that they are commonly colonized by different lichen communities. The main goal of this contribution is making a diagnosis of alterations that lichens may cause in ceramic materials, as well as to determine the possibilities of removal by treatments based on laser irradiation and use of biocides.Geomateriales 2 (Ref. S2013/MIT-2914, Regional Government of Madrid and EU structural funds) and IPERION-CH (Integrated Platform for the European Research Infrastructure on Cultural Heritage (Ref. H2020-INFRAIA-2014-2015 nº 654028).Peer Reviewe

Effect of biological colonization on ceramic roofing tiles by lichens and a combined laser and biocide procedure for its removal

Biodeterioration damage is an important issue in conservation and restoration of built heritage, especially when ceramic materials are used. Biological colonization of ceramic roofing tiles by lichens is a common phenomenon. However, there are no reports to date of lichens removal from unglazed roofing tiles for conservation purposes. This paper for the first time reveals the results of a combined procedure undertaken to assess the removal of lichens on different kinds of unglazed ceramic roofing tiles by treatments based on both dual sequential laser irradiation and treatment using Acticide CF biocide. Three species of lichens were identified: Verrucaria nigrescens, Calogaya decipiens and Pyrenodesmia teicholyta. The chemical and mineralogical composition of roofing tiles were characterized by X-ray fluorescence (XRF) spectrometry, optical polarized petrographic microscopy, and X-ray diffraction (XRD). Laser irradiation was accomplished by applying sequences of nanosecond laser pulses at two wavelengths (1064 and 266 nm). After dual sequential laser irradiation a biocide was applied. To assess the combined effect of both treatments several techniques were used, including stereo and fluorescence (FM) microscopies, scanning (SEM) and transmission (TEM) electron microscopies, and FT-Raman spectroscopy. Chemical composition of the analyzed roofing tiles was shown as a relevant factor regarding the degree of interaction between the biological colonization and the substrate, and hence, the bioweathering effect. The combined procedure has proved to be very effective in ablating cortical layers in all species, or even complete areolae in V. nigrescens, enhancing biocide effect in the thalli of C. decipiens and P. teicholyta, and producing the complete damage of both bionts.Peer Reviewe