Analytical characterization of biodegraded wood from a 15th century Spanish cloister

Chemical changes observed in wood as a result of fungal decay have been studied. The development and transformation of the decayed wood was evaluated by thermal analysis (thermogravimetry) and derivative thermogravimetry and scanning electron microscopy. Samples of wood beams showing different deterioration stages from the coffered ceiling of the cloister of St. Francesc (15th century) (Palma de Mallorca, Spain) were characterized. As decay develops, cellulose and lignin disappear and inorganic salts are formed. Furthermore, the secretion of oxalic acid by fungi and the presence of organic pollutants lead to the precipitation of authigenic salts. Therefore, the biomineralization process is strongly favoured by fungi that act as calcification nuclei. At the final stage of fungal colonization, crystals of calcium salts appear in the surroundings of decayed wood fibres. The thermal behaviour of these samples is the consequence of biodeterioration and weathering processes.