An experimental study on the influence of surface finishing on the weathering of a building low-porous limestone in coastal environments

Limestones used as building material are especially prone to weathering in coastal environments due to interactions between sea mist and the carbonate stone. Subtle variations of the commercial surface finishing may lead to differences in decay patterns and aesthetic properties due to salt crystallization. To explore this potentially contrasting behavior, tablets of rough and polished low-porous limestone were aged in a sea-salt spray corrosion chamber to simulate their exposure in a coastal environment. Different crystallization morphologies and relative proportions of soluble (halite) and less soluble (gypsum) salts were observed in the aged rough and polished surface samples. These morphologies are ascribed to the microtextural characteristics and the surface pore systems of the diverse (rough and polished) substrates that in turn influence fluid (saline solution) transport toward their interior, as well as the different salt solubilities interacting with the substrates. Polished surfaces exhibit little evidence of damage after the ageing test in contrast to the rough samples but do have conspicuous gypsum on the surface together with halite. The scarcity of gypsum on the rough surfaces, in addition to a more severe change in the porosity system, suggests that salts penetrate deeper when the stone surface is not polished. Potential decay induced by salt crystallization pressure is therefore minimized when the stone surface is polished. However, polished surfaces show more significant changes in luminosity and chroma after the ageing test, and so are less attractive from an aesthetic point of view. Surface finishing is thus an important feature that needs to be characterized for a better understanding of the weathering behavior of building stones used in coastal environments.