Biodeterioration of stone: a review

Porous Materials Water in Porous Materials Flow in Porous Materials Unsaturated Flows Unsaturated Flow in Building Physics Composite Materials Evaporation and Drying Topics in Water Transport Appendices Symbols Used Properties of Water Minerals, Salts and Solutions Other Liquids Other Data

Water Transport in Brick, Stone and Concrete

The evidence presented by numerous investigations of the interface between lichens and their rock substrates strongly suggests that the weathering of minerals can be accelerated by the growth of at least some lichen species. The effects of lichens on their mineral substrates can be attributed to both physical and chemical processes. The physical effects are reflected by the mechanical disruption of rocks caused by hyphal penetration, expansion and contraction of lichen thallus, swelling action of the organic and inorganic salts originating from lichen activity. Lichens also have significant impact in the chemical weathering of rocks by the excretion of various organic acids, particularly oxalic acid, which can effectively dissolve minerals and chelate metallic cations. As a result of the weathering induced by lichens, many rock-forming minerals exhibit extensive surface corrosion. The precipitation of poorly ordered iron oxides and amorphous alumino-silica gels, the neoformation of crystalline metal oxalates and secondary clay minerals have been frequently identified in a variety of rocks colonized by lichens in nature. For a better understanding of the impacts of lichens on environments, further work on the comprehensive involvement of the lichen effects on weathering of natural rocks, deterioration of building stones and stonework, and formation of primitive soils should be carried out.

http://www.geo.mtu.edu/KeweenawGeoheritage/BlackLavas/Hunters_Point_files/ChenetalCatena.pdf

Weathering of rocks induced by lichen colonization — a review

A review of wind-driven rain research in building science

The present overview on salt-induced deterioration of inorganic porous materials focuses on those topics considered the most relevant for understanding this phenomenon. These are movement of both water/moisture and salts within the pore system; influence of the presence of salts in moisture absorption; effect of the simultaneous presence of more than one salt; salt distribution in masonry; deterioration mechanisms; and weathering patterns. Of the latter, the most ubiquitous are powdering and scaling, and they have been found to occur on most stone types. However, the mechanism that induces the same outward appearance on different stones can vary significantly depending on the synergism that develops among porous material, salt, and moisture.

Salts in the deterioration of porous materials: an overview

The origin of calcium oxalates on historical buildings, monuments and natural outcrops

Wetting, deterioration and visual features of stone surfaces in an urban area

A problem regarding Roman imperial monuments is the presence of patinas, rose-brown in colour, covering the external surface of marble, called ‘scialbatura’. Different hypotheses have been advanced to explain the origin of these patinas; that which refers scialbatura to treatments applied to the monuments with the aim of protecting the stone is the most accepted one. We have studied these patinas on a wide series of monuments, historic buildings, artifacts and natural outcrops, on both marble and limestone, exposed to the open atmosphere. An origin linked, either directly or indirectly, to external treatments for protection is rejected: the so-called scialbatura is found to be due to the biochemical activity of encrusting lichens.

A study of the patina called «Scialbatura» on imperial roman marbles

This is the first report of a large deposit of weddellite (CaC2O4-2H20), the formation of which is still in progress. Mineralogical and physical characteristics of this mineral were studied and the origins of its formation established. The presence of weddellite is rarely reported in natural outcrops, has controversial origins, and has always been found in very small quantities. Thus, in natural environments, the stable form appears to be calcium oxalate monohydrate (whewellite) of which there is evidence of wider diffusion. In our case, weddellite is the main component of the alteration affecting every marble surface on the Isle of Torcello in the Venetian Lagoon. Ita origin must be related to the presence of numerous Cyanophites, whose role is to provide the system with oxalic acid, which in the presence of a carbonatic substratum precipitates in the form of calcium oxalate dihydrate. The enormous proliferation of these perforating “algae”, as of other endemic species, is connected to characteristics that are most peculiar to the Venetian Lagoon.

Marco Del Monte

Papers

The origin of calcium oxalates on historical buildings, monuments and natural outcrops

Wetting, deterioration and visual features of stone surfaces in an urban area

A study of the patina called «Scialbatura» on imperial roman marbles

Weddellite on limestone in the Venice [Italy] environment.

Chemical and biological weathering of an historical building: Reggio Emilia Cathedral