Stone Deterioration on the Tower of Belem / Zerstörung des Natursteins am Turm vom Beiern

The Tower of Belem was constructed using the local Lioz limestone. The stone, in its "typical" variety is very compact and durable. However, different levels in the quarry produce varieties of poorer quality which can vary substantially from it. The presence of iron oxides gives rise to coloured varieties of this stone. The stone may contain many large fossils and also clay-bearing stylolites. The presence of clays in the stone makes it more susceptible to deterioration and, according to their distribution, results in different deterioration patterns. This paper describes the various deterioration patterns found on this structure and their origin. Even the most severe deterioration observed, powdering and flaking, affects mainly the immediate surface, while the stone underneath maintains its compactness.