Environmental Decay of Ignimbrite Patrimonial Monuments in the Dry, Urban, and Non-Industrial Atmosphere of Morelia (México)

Damage to the rocks of historic built heritage needs to be addressed to facilitate their conservation and restoration; the most serious damage is caused by environmental conditions and human activities. Buildings constructed with ignimbrite blocks bonded with lime mortar in Morelia, México, a UNESCO World Heritage site, were studied. The damage mainly occurs in the facades, on the surfaces of the rocks and in the mortar of the union exposed to climatic factors such as sun, rain, wind, and temperature changes, due to the actions of humans and vehicles emitting polluting gases; and due to pigeon excrement. This has caused the formation of patinas and flora, reduced the mechanical strength and exfoliation, decreased the density and cohesion in the mortar with rocks, and led to friction damage caused by people. In the facades of five buildings, the mechanical resistance and microstructural characteristics were indirectly determined by XRD, XRF, and SEM. The results were related to the climate, humans, and vehicular pollutant emissions. The damage was due to the environment, the influencing geographic orientation, and prevailing winds, rising capillary water on the facades, pigeon droppings, vehicular pollutant gases, and humans. Potential banks of healthy quarries were analyzed for use in the conservation and restoration of damaged monuments.