Stone has been employed in construction for at least five millennia. The ancient Egyptians were the first to widely exploit stone for building, exploiting the rich stone resources of the Nile Valley. Greek and Hellenistic traditions grasped the potential of, especially, marbles and limestones. Subsequent stone building to the present day is deeply rooted in these early traditions. Because many buildings are irreplaceable statements of the development of human cultures and civilisations, an active architectural conservation movement has developed to address this complexity of problems.
Limestones in the Built Environment (LBE) leads off with a description of the complexities of limestone weathering (Smith et al.). It debunks the general preconception that it proceeds in a slow, uniform and predictable way by the action of acid rain on exposed surfaces by introducing the role played by environmental sulphur, nitrogen oxides and a variety of salts. Limestone durability is also a function of density, porosity and composition. Causes of catastrophic decay in granular limestones are usefully discussed.
Around half the papers are case histories treating a wide range of issues. For example, Cassar provides a thorough presentation of Maltese limestones, particularly the Oligo-Miocene Globigerina and Coralline Limestones, the dominant building stones from the Neolithic through Phoenician, Roman and Arab phases of history to the present day. Other case studies include the characteristics of the Maastricht limestones and the role of moisture content in the catastrophic failure of Oxford college walls of mixed limestones by resistivity methods.
LBE also includes a number of essentially laboratory studies. Detailed mechanisms of aggressive salt damage were investigated on a variety of limestones where drying and crystallization from supersaturated pore solutions are causal (Espinoza-Marzal et al.). Ruiz-Agudo et al. explain the effects of borax on the crystallization of sodium and magnesium sulphates.
Limestone replacement in Greek monuments (Stephanides), particularly of fossiliferous Plio-Pleistocene rocks, results in deterioration (Smith et al.). A rigorous investigation of pore structures in Portuguese Middle Jurassic dimension stones (Figueiredo et al.) explains their durability. The main methods of study employed were scanning electron microscopy combined with mercury injection porosimetry.
Calvo et al. range widely around the shores of the Mediterranean describing marbles, fine-grained and shelly limestones, travertines and brecciated carbonates country-by-country. Siegesmund et al. have crafted an impressively detailed presentation of German limestones, from Devonian to Holocene. Images of thin sections are usefully combined with test data on diverse criteria. Finally, there are four informative papers on materials and treatments.
The title of the Natural Stone Resources for Historical Monuments (NSR) misleads in that only eight papers directly address this subject. The resurgence of interest from the later decades of the last century, particularly in the use of stone in quality and prestige developments, has highlighted the problems of supply. Resistance to the opening of new quarries, the reopening of older stone pits, and local and government regulation have led in many cases to repairs in material other than the original.
Přikryl et al. address this problem with a case study of the restoration of the 14th to 15th Century Charles Bridge in Prague. The closure of all quarries that supplied the original sandstones led to 20th Century repairs in a variety of unsuitable substitutes. Testing for durability and cosmetics of samples from these sites has led to the identification of a pair of new sites that may be exploited. Romer tuff from the Eifel region of Germany (Nijland et al.), extensively used in Dutch monuments from Roman times onwards, is a similar example. Limited availability has led to the evaluation of a trio of Italian tuffs, one of which meets aesthetic and physical requirements for restoration use.
Structures in the Fruili–Venezia Giulia region of NE Italy uses a considerable diversity of Ordovician to Pliocene rocks. Sources of dimension stone in the region and the numerous quarries working them are well known, but the data are widely scattered. Frangipane describes the creation of a database intended to bring all the information together in structured form to provide a cross-disciplinary resource, particularly for architects. Kampfova et al. describe a similar, but highly structured and complete, electronic database documenting historical dimension stones used in the Czech Republic.
Despite its title, NSR also includes nine weathering studies. The honeycomb and cavernous (alveolar) weathering of Cretaceous sandstones in Saxony, the interaction of black crusts with three French limestones and the effects of fire on the trachyte of the Tepla monastery in the Czech Republic are three contrasting studies of dimension stone damage. Laboratory studies, predominantly on the effects of salts and salt crystallization, examined, as examples, a French Eocene detritic limestone, a wide range of igneous and sedimentary lithologies, tuffeau and Sebastopol stone (both limestones), and Portuguese Middle Jurassic dimension stones.
Laho et al. examined the Middle Miocene Leitha limestones that have been widely employed in the Bratislava region of Slovakia. This is probably the clearest exposition of the association between variations in pore spaces, pore volumes and water absorption to weathering properties. A related study (Adriani et al.) on Miocene and Pliocene to Pleistocene calcarenites and tufas in the Apulian region of southern Italy showed similar results.
In welcome contrast is Cooke's account of the Corsi Collection in the Oxford University Museum in the identification of ornamental stones, chiefly marbles, employed in building sculpture and the decorative arts. The collection includes over 300 sample blocks drawn from the monuments of ancient Rome in its total of around 1000 items and is the richest collection of its kind.
McCabe et al. provide a detailed sequential account of three Carboniferous Ballycastle sandstones in Bonamargy Friary quarried in the area of the Fair Head sill in NE Co. Antrim, N. Ireland. A history of the fabric documents its construction in 1500, destruction by fire in 1584, accelerated frost damage in the Little Ice Age between 1590 and 1850, repair in the early 17th Century, final abandonment in 1639 and unsuitable conservation interventions in the 20th Century.
Šťastná et al. describe methods that have been successfully employed to differentiate Mediterranean white marbles, but marbles in the Bohemian Massif in the Czech Republic present a new range of problems. Raman microspectrometry applied to reduced carbonaceous matter in these marbles identified three groups directly related to metamorphic grade. The authors believe that the method could add a useful new diagnostic to provenancing carbonaceous marbles.
Taken together, these two volumes present a considerable body of knowledge and experience, but with much repetition on weathering processes and a considerable body of mixed experimental outcomes. Almost all are directed at conservation practitioners, but faced with such a broad and diverse literature, most architects and contractors would have considerable difficulty identifying a starting point. The need for an integrated source embracing all major characteristics of dimension stone emerges starkly.