1. Maintenance and Conservation of Materials in the Built Environment

Materials on the built environment are exposed to several agents that promote alteration processes resulting in features that might be considered detrimental of its value. Here we review the main issues related to the struggle against these alteration processes, from the consideration of the intervention criteria, including the non-intervention option, to strategic considerations on the organisation of the intervention that must consider the temporal and spatial features of the alteration processes, as well as possible interventions on the surroundings of the materials, e.g. atmosphere, terrain and structure, and in relation to treatments of materials, including its replacement. It is highlighted the problem of testing using small clean specimens aggravated by comparative studies based on one specimen by case. Assessment of short-term an effects is discussed in relation to intrinsic aspects of the interventions. The long-term effectiveness is linked with the global strategy namely in relation to the conditions that promote the alteration processes. Some sustainability questions related to the intervention operations are also considered such the use of toxic substances and the consumption of resources.