Conservation of building materials of historic monuments using a hybrid formulation

Green volcanic tuff has been used in the construction of very important historic buildings in the city of Guanajuato, Mexico, a UNESCO World Cultural Heritage city since 1988. The chemical and mineralogical composition as well as the physical properties observed in the stone (Loseros tuff) presently used to restore such buildings suggests the need for preventive treatment to delay the decay process. A hybrid formulation based on tetraethyl orthosilicate (TEOS), colloidal silica, and hydroxyl-terminated polydimethylsiloxane (PDMS-OH) has been used to treat the volcanic tuff. Several studies were performed in order to evaluate the properties of the stone after treatment; such as determination of the percentage of formulation deposited, as well as variations in porosity, hardness, and salt crystallization resistance.