Modelling the rapid retreat of building sandstones: a case study from a polluted maritime environment

Abstract

Sandstones are widely used as building stones throughout NW Europe. Unlike limestone, sandstones tend to experience episodic and sometimes rapid surface retreat associated with the action of salts and often leading to the development of hollows/caverns in the stone. The unpredictability of these decay dynamics can present significant problems when planning conservation strategies. Consequently, successful conservation requires a better understanding of the factors that trigger decay and determine the subsequent decay pathway. An overview of results from previous studies provided the basis for simulation experiments aimed at identifying the factors that (a) initiate decay and (b) permit the continuance of salt weathering despite rapid loss of surface material. These simulation studies involve investigation of changes in micro-environmental conditions as surface hollows develop and examination of salt weathering dynamics within such hollows. These data combined with knowledge gained from previous work have allowed the refinement of a conceptual model of rapid sandstone retreat. In this model decay is linked to the establishment of positive feedback conditions through interactions between factors such as porosity, permeability, mineralogy and their effect on salt penetration.

Morphology and detachment mechanism of weathering crusts of porous limestone in the urban environment of Budapest

“…Smith et al (2002) have documented that black crusts can also develop on sandstone, but catastrophic decay occurs mostly on isolated ashlars without spreading from one to the other. The major difference between the decay mechanism of sandstone and porous limestone is in the dissolution and re-precipitation process.…”

“…Kieslinger 1949;Amoroso and Fassina 1983). The most common form of weathering on limestone is the development of gypsum crusts, as has been known from many cities (Amoroso and Fassina 1983;Antill and Viles 1999;Lefèvre and Ausset 2002;Fassina et al 2002;Smith et al 2002Smith et al , 2003Török 2002;Thornbush and Viles 2004;Török and Rozgonyi 2004;Smith and Viles 2006;Török et al 2007). Crust formation is mostly attributed to the transformation of calcium carbonate into calcium sulfate.…”

Dimension stones of the North Hungarian masonry arch bridges

“…Fine-grained sandstone ashlars show typical weathering features such as scaling and flaking that are very similar to sandstone described from other parts of the World (Turkington and Paradise 2005;Warke et al 2006). The damage is related to freeze-thaw cycles, or in some cases, to salt-induced or thermal cycles (Smith et al 2002). Due to the location and environmental factors the sandstones of the studied bridges are mostly affected by freeze-thaw cycles and thermal insolation cycles, rather than salt-induced weathering.…”

Salt-weathering simulations under hot desert conditions: agents of enlightenment or perpetuators of preconceptions?

“…This regime proved very effective at reproducing phenomena, such as multiple flaking, that are frequently observed in cavernous hollows. Subsequent analysis of salt penetration within the three sandstones used in the study by Smith et al (2002) showed marked differences that could be related to the physical properties of the stone (Fig. 2).…”

“…However, following on from studies that constructed chambers to simulate wet and dry deposition of acid pollutants on building stones (e.g., see Johnson et al, 1990), commercially available salt corrosion cabinets can now be used to create a fine saline mist that ensures uniform deposition of known amounts of salt solution onto test blocks. For example, Smith et al (2002) used a corrosion cabinet to repeatedly deposit a 10% magnesium sulphate aerosol onto different quartz sandstones that were then subject to bNegevQ type heating and cooling cycles (Goudie, 1993). This regime proved very effective at reproducing phenomena, such as multiple flaking, that are frequently observed in cavernous hollows.…”