Evaluation of Portuguese limestones’ susceptibility to salt mist through laboratory testing

The salt mist present in the coastal shoreline constitutes an important weathering agent of the building materials applied in these regions. Portugal has an extensive coastline, which has a high population density. It holds a long tradition in the use of stone as a building material, due to the abundance of this natural resource, but also because of its durability and beauty. Considering the main ornamental stones mined in Portugal, limestones are the most susceptible to the action of saline atmospheric aerosol, because, in most cases, they present open porosities higher than those of other stone types. This feature facilitates the penetration of saline aerosol in their structures. Six widely applied Portuguese limestones, with different technological properties, were selected for this study. After accessing their petrographic and main technological features, the limestones were submitted to salt mist test. The test method, established in the respective European standard, was complemented with further determinations (variation on water absorption and flexural strength after salt mist cycling). The results allowed evaluating the limestones’ suitability for the main types of applications and for specific usage conditions, within each one. Thus, it was possible to set the recommended uses for each limestone, in order to maximize its durability. Salt mist testing made possible to determine the limestones’ resistance to the climatic conditions of coastal areas. The detailed analysis of the salt mist results strengthens the knowledge that the open porosity plays a decisive role in the limestones’ behaviour to this test.