sentences:  Sydney's significant sandstone buildings, such as Sydney Hospital, have required the attention of these expert stonemasons, as most of Sydney's sandstone buildings date from the 19th century.For example, in 2012, conservation work was done on the sandstone of the clock tower of Sydney Town Hall as part of a four-year, $32 million project to restore the building.The capitals on top of the tower columns needed replacement because they had been badly affected by weather and pollution.