Salt fog experiments on natural stone: The case of three Portuguese ornamental limestones

The saline fog is one of the main degradation causes of the built historical and recent heritage. The effect on natural stone is one of the main concerns of the producers and installers of these materials, whether caused by non-aesthetic aspects either by the economic implications that results in.

There has been a growing demand of the industry of the natural stone sector to submit their rocks to salt spray tests. Thus they can get a better understanding of the response of their stone materials when exposed to this degradation agent.

There are several studies on the effects of salt spray in various materials. As example there are works in ornamental granites [1, 2, 3, 4, 5], in carbonate rocks [6, 7, 10, 11], structural ceramics [8, 22], rocks with application of consolidants and water-repellent products [9], concrete [12], steel [13] and studies of samples from monuments [14, 15].

In this study three Portuguese ornamental limestones currently commercialized and with great application in outdoor and indoor environments were used. The limestones commercial designations are Branco Valongo (BV), Gascoigne Beige (GB) and Moleanos (CRM). Samples with polished finishing were exposed to 60 cycles of salt spray. Mass variations were recorded before and after the test and the alterations in the surface were photographically recorded. The results compare the performance of these natural stones when subjected to the action of the salt mist.

It is considered that these accelerated alteration laboratory tests are essential to increase the knowledge of these materials in order to be able to predict their performance in works in order to avoid unpleasant situations for ornamental stones installers and end users.