Compatible Air Lime Mortars for Historical Tiled Facades: Bond and Mechanical Strength versus Tile–Mortar Interface Microstructure

Abstract

Exterior old glazed tiled facades have been a very important heritage testimony of Portuguese culture and traditions throughout the years. The adhesion of the mortars to the old tiles is a very important factor in the behavior of the tiled facades. This study performs a mechanical and water behavioral characterization of compatible air lime (AL) mortars with old substrates and tiles and a microstructural characterization of tile/mortar interface to evaluate the bond between the materials. Formulated lime mortars present mechanical strength values that provide compatibility. Compressive strength varies between 0.42 and 0.61 MPa in AL-based mortars and between 1.09 and 1.60 MPa in lime metakaolin (MK) mortars. Ca/Si evolution by EDS analysis provides indications on penetration of lime paste into ceramic biscuit. Higher Ca/Si values result in higher bond strength values.