Difficult decisions regarding maintenance, repair, or replacement of traditional materials are often constrained by conflicting preservation goals, limited resources, and an unpredictable climate. A basic understanding of how traditional building materials of wood, stone, lime, clay masonry, and metals are first created and then destroyed by natural and human intervention can inform these difficult decisions. This session will focus on understanding the impact of various forms of moisture (humidity, rain, and flooding) and on developing effective strategies to prevent or mitigate damage to historic materials.