AIC's 52nd Annual Meeting

Salts found in buildings and monuments are ionic compounds that can dissolve in water. When the water evaporates, they crystallize as hydrated molecules which increases their volume, emerging as efflorescence that generates chemical and physical changes in the porous systems of various types of masonry. Damage to masonry from salts can both greatly disfigure the surface of the masonry visually, but also deteriorate the material to the point where it becomes structurally unstable. The main factor that effects how salts crystallize and form efflorescence in porous systems is the frequency and speed of wetting and drying cycles. While weather cycles are the most common drivers of wetting and drying cycles, routine cleaning and/or wetting from sprinkler systems can also contribute to these cycles. Additionally, there are other factors that must be taken into account to understand/determine the content of salts and how aggressive/disruptive they can be to the porous system.

This paper establishes a synthesized protocol that will help identify soluble salts in monuments and buildings by analyzing multiple factors that are either external or inherent to the object of study (monument/building), as well as identify the agents and mechanisms of degradation. This proposed protocol has been developed using one (1) of several stone columns that supports the colonnade that encircles the market of Sant Andreu in Barcelona as a case of study. This market colonnade was likely built between 1914 and 1923 and is composed of fifty (50) columns. The column chosen as the subject of this study was diferentially affected by salt efflorescence compared to the adjacent columns. The subsequent research protocols discussed in this paper aimed to identify why this was so.

While examining and analyzing soluble salts/efflorescence is not new to the fields of conservation and building science, the author developed a synthesized approach after researching a range of investigation and examination techniques used across a variety of different countries. Many analysis techniques are very complicated and/or focus on one aspect of the salts rather than the site as a whole. While developing this protocol, the initial phase included a study of the structure of the colonnade and the column, the compositive materials of these (with POM), as well as the environment and climate. During the second phase, both dry and wet samples of salts were extracted from the stone for analysis. The wet samples were analyzed with an instrument to determine their ionic concentration as well as analyzed with chemical reagents to qualitatively identify sulphates, chlorides, nitrites and nitrates. The dry samples were encased in polyester resin and observed under POM and SEM. After having reviewed and evaluated the different techniques available and utilized globally by the field, these protocol steps were selected so that the average conservator could use them in their practice, even with relatively limited access to high-tech instruments, and still produce results that guide best practices for mitigation of damage due to soluble salts/efflorescence.