In ideal environments, most common construction materials are very durable and can last indefinitely. However, design or construction deficiencies or lack of proper maintenance can result in less-than-ideal conditions under which construction materials will degrade. Degradation can take many forms, including chemical reactions, consumption by living organisms, and erosion or mechanical wear. Traditional building materials – steel, concrete, and wood – usually deteriorate and fail via well-known mechanisms. Even innovative materials that appear on construction sites can degrade, either by these well-understood mechanisms or through exotic, sometimes surprising, reactions and processes.