Abstract
There are several aspects of maintaining the quality of stonework in buildings in urban environments. Two of the most important factors are the durability of stone and the way in which the environment affects the weathering of stone in general, especially the relative affects of natural and pollution weathering. In addition the severity of the conditions to which a stone is exposed depends upon its location within the building itself.
Urban atmospheres have generally been polluted with acidic gases and such polluted air is believed to accelerate the process of weathering by many times compared with that in natural rural environments. The effects of this weathering can be both conspicuous and unsightly and include pitting, blistering, spalling and cracking.
The general resistance to weathering of sandstones is determined by their chemical compositions. In particular, those sandstones which contain carbonate cements are susceptible to attack by acid rainwater. This occurs through solution of carbonate matrix, allowing many grains of sand to loosen and be removed, even over a relatively short time period.
In terms of assessing the durability of sandstones, the tests are more straightforward than those, for example, for limestones. In fact the durability of sandstones can be assessed using two types of acid immersion tests, followed by two types of crystallization tests. The results of these tests allow the sandstones to be classified for use in different environmental conditions and locations in buildings.
