The consolidation work involved removing all Portland cement mortar joints, restoration, and pointing the stone work with more appropriate lime mortar, sealing all cracks that allowed infiltration of water, and consolidating the decorative mosaics that were detaching from the façade.
The cleaning operation removed various types of dirt, some from biological activity, some water-born substances, and some anthropogenic. Particular attention was given to removal of air-born particles, a byproduct of modern consumption of fossil fuels, which deposit layers called “black crusts.”
These crusts are a combination of substances that include soot, oils, dust, and other chemicals, such as sulfur dioxide, that not only heavily stain the material but also, when combined with water, create an acidic solution that corrodes very aggressively limestone and other minerals composed of calcium carbonate.
The last phase of the restoration was various treatments to the masonry to reduce biological activity, seal the stone and mortar joints, and “velatura” subtle color layers to give the restored stone work a homogeneous appearance.