Restoration of the Sistine Chapel frescoes smoke and exhaust fumes of the city, being "much dirtier than the ceiling proper". The building was a little unstable and had already shifted considerably prior to Michelangelo's work of 1508, causing cracking of the ceiling, the crack in the "Judith" pendentive being so large that it had to be filled with bricks and mortar before painting. The upper part of the ceiling provided Michelangelo an irregular surface due to cracks and water seepage. Continued ingress of water from the roof and from unroofed exterior walkways above the ceiling level had caused seepage which carried down salts from the building
Sistine Chapel exterior can be seen only from nearby windows and light-wells in the palace. Subsidence and cracking of masonry such as must also have affected the Cappella Maggiore has necessitated the building of very large buttresses to brace the exterior walls. The accretion of other buildings has further altered the exterior appearance of the Chapel. The building is divided into three stories of which the lowest is a very tall basement level with several utilitarian windows and a doorway giving onto the exterior court. Internally, the basement is robustly vaulted to support the chapel. Above is the main space, the Sistine