Exposure to the weather and the way a building is used alters the equilibrium between “external cladding, plaster and finishing coat”. This phenomenon leads to deterioration and disintegration of the plaster and a loss of its mechanical properties, making it impossible to maintain the static and functional quality. Such disintegration and deterioration can also derive from direct or induced mechanical stresses. Much of these depend on the moisture present in the masonry, both derived from external (rainwater) and internal causes (vapour diffusion). These phenomena can cause changes in state and micro-variations in volume (freeze-thaw) and chemical and electrochemical phenomena (efflorescence, oxidation, chemical incompatibility). In the end, these can lead to physical pathologies (wash away, risk of cracks and fissures, swelling, mechanical erosion, detachment, disintegration) and biophysical pathologies (mould, mildew, algae and corrosion).