Review on Decay Factors and Decay Patterns of Carbonate Sedimentary Stones in Historic and Cultural Open-Air Sites

The number of historical open-air sites built of stone are relatively limited in comparison to the other historical sites in Iran, but these sites include great significance in terms of value, history and their undiscovered aspects. Since these stone open-air sites are generally about two thousand years old, they have been exposed to decay factors for a long time. Many information and data on the types of decay factors and their patterns are scattered in the articles and books generally available in English access to which is limited for experts in the field of conservation and restoration. This study attempted, through purposeful data from research on the open-air sites and monuments, to effectively address all aspects of the deterioration of carbonate sedimentary stones which constitute the majority of Iran’s sites. In this way, using library references, environmental factors and common decay patterns in similar climate and industrial conditions are discussed. It has become clear from studies that, contrary to the impression, “environmental factors” are not only the factors in the deterioration of sedimentary stones, but also the physical and chemical properties of the stone (Intrinsic problems) are very important in the term of decay. Among the chemical and physical decay factors, chemical factors in deterioration are more important because they lead to the dissolution or alteration of the nature of the stone.