The Walls of Gubbio exhibit several issues related to the materials degradation (limestone, travertine, sandstone-serena stone, plasters, binders) used for building and restoration. These materials suffer of increased deterioration due to climate change effects coupled with pollution. The degradation effects of the outer surface are:
- loss of material (formation of hollows, differential degradation, erosion, gap, lacking, pitting)
- decay of the material cohesion (disintegration, pulverization)
- loss of continuity perpendicular or parallel to the outer surface (fracturing/cracking, peeling, warping, swelling, scaling)
- addition of foreign material (concretion, “black crusts”, surface deposit, efflorescence, scaling, stain, film formation)
- colour variations (discoloration and patina).
Another predominant erosion issue is the gradual degradation of the mortar binding the Walls. The degradation/reduction of the mortar entails the loss of homogeneous distribution of stress on the stone surfaces and leads to a heterogeneous stone-binder system behaviour.
Blackened stone areas on the Town Walls (left). Erosion due to rainfall and degradation of mortars of the Town Walls (right).
