The decay processes in monuments, considered as interaction between building materials and environmental factors, presents a specific interest in the case of marine environment (Mediterranean), in mild climatic conditions An extended monument, like the Medieval Fortress of Rhodes could be a characteristic example. It is constructed by a susceptible to salt decay biocalcareous porous stone which suffers mainly from salt crystallisation and hard carbonate crusts formation.

The research program has been developed on walls of different typologies, according to their position and exposure orientation to various environmental factors, and specifically concerning humidity sources as capillary rise via ground and marine salt spray. Stone samples from different positions along the fortress, at various heights and depths on the walls, significant of the main decay patterns (alveolar, carbonate crust and mixed), underwent physical and chemical examination.

Humidity and soluble salts' concentration measurements by Atomic Absorption Spectroscopy, Ionic Chromatography and specific conductivity allow the assessment of their distribution patterns on the masonries.

Hence from the correlation between environmental factors and the material properties, directions for a conservation plan might be derived.

Acoustic techniques have always had an important presence in monument conservation. A first evaluation of the formation of cavities and/or inhomogeneities is commonly done by finger rapping and ear listening, to discover acoustical variations in the transmission of sound waves. We have characterized the size of the cavities in several materials, as stones, rocks, mural paintings and stucco, by using 7 kHz sound waves generated by a piezoelectric transducer. The experimental set-up developed for these purposes allows, through the analysis of the waves' delay times, to detect cavities and/or inhomogeneities as small as 4 cm in diameter. The design of the instrument, its capabilities and potential applications are documented.