Stone Deterioration Research Articles

Millennium-long damage to building materials in London

Damage functions from a range of sources are used to estimate deterioration of carbonate stone, iron and copper, in addition to the rate of blackening of stone surfaces in London across the period 1100–2100 CE. Meteorological and pollution input is available for only a relatively short part of this span, so non-instrumental weather records and modelled pollution are utilised for historic values, while future climate is adapted from the HadCM3A2 model output and pollution assessed from likely regulatory trends. The results from the different damage functions compare reasonably well showing comparable changes in damage rates with time. A potential square-root dependence of change in deposition velocity of SO 2 to limestone suggests a possible overestimate of damage when pollution is high. Deterioration is especially intense from the 1700s. It is difficult to be certain whether the corrosion of copper accelerated as early as this or it developed in the 20th century. Nevertheless all the functions predict a decline in copper corrosion from the end of the 20th century. A blackening function was developed to relate elemental carbon concentration and the colour of deposited particulate matter to blackening rate, which suggests that soiling was particularly rapid in the late 19th century. The increase and subsequent decrease in damage to building materials is interpreted in terms of a Kuznets curve. The centuries where pollution controlled damage to durable building material seems to be over. Weathering, in a changing climate may have the greatest impact in the future.

Examples of weathering and deterioration of Tertiary building stones at St. Michaels Cathedral in Cluj-Napoca (Romania)

St. Michaels Cathedral is one of the oldest Gothic architectural monuments in Cluj. It is built predominantly of Cenozoic (Eocene) limestones which were deposited on a shallow carbonate platform. They are composed of different facies and microfacies types with varying amounts of particles, matrix and cement. Limestones from the Baci quarry (Cluj Limestone), which is situated about 3 km from the centre of Cluj, were commonly used. The weathering features correspond to the microfacies types, to the position of the stones in the walls and to the exposure (east, south, west, and north), which controls the moisture/dry cycles. This interrelationship is documented by macroscopic and microscopic examples of the decay of samples analyzed from the lower part of the walls. General parameters for a correct classification of carbonate rocks and their importance for weathering are discussed. The general mechanisms of weathering (thermal expansion, water uptake, freezing, chemical weathering) are described. The migration of moisture (capillarity) and the formation of crusts of varying mineralogy on the surface of building stones are documented. Macroscopic description of damage includes the decay into plates and flakes, the formation of crusts, the formation of fractures, and the growth of lichens and microorganisms. The microscopic analysis documents characteristic damage in detail: fractures parallel to the surface of the stone, internal cementation of fossil chambers (micro-nodules), repeated formation of crusts in varying generations, fracturing in intensively lithified, rigid limestones, and settling of lichens in different positions. Furthermore, different historical mortars and modern “concrete-mortars” and their behaviour in comparison to the adjacent limestones are briefly discussed. The possible conservation and restoration of weathered limestones in St. Michaels Cathedral are discussed with regard to the most recent conservation methods. The advantages and disadvantages of surface conservation by silica ester, hydrophobic substances as well as by epoxy resin are also dealt with. Special methods for conservation (acrylic total impregnation, lime slurry, biological lime slurry) and DIN-methods as well as analysis of the success of the methods used are presented in a short summary.

Moisture sorption behaviour of salt mixtures in porous stone

Moisture in stone material is the key factor for all stone deterioration processes and also in weathering of cultural heritage. With additional presence of salts in the material the situation gets even more critical. While the properties of pure salts with moisture are well known, knowledge about the interaction of salt mixtures with moisture is still poor. In different approaches the reactions of salt-contaminated stone material on changing moisture were tested in the laboratory. Experiments with different solutions in the Na–Mg–SO 4–NO 3–H 2O system revealed interesting new results on the moisture behaviour of salt-contaminated samples. Theoretical considerations and computer simulations are helpful to interpret the data obtained, but are not yet sufficient to explain the real processes acting on site at the monuments. More encouraging to this fact are complementary studies on visible efflorescences in the same salt system. It is shown how by experimental approaches the understanding on salt-induced stone deterioration is strongly complemented.

Deterioration of limestone structures associated with copper staining

Sixty limestone monuments in Central London, UK, with copper staining from brass or bronze attachments, were surveyed. Severe spalling was noted at some copper-stained sites. The survey suggests that copper initially protects the surface, but causes stone deterioration after around 70 years. Samples from four limestone monuments were analysed microbiologically and using ESEM/EDX. EDX analyses suggested the build-up of salts below a basic copper carbonate skin (salting) as the most probable explanation of the observed deterioration. Copper-stained stone was free of photosynthetic microorganisms and yielded relatively few other microorganisms. ESEM and EDX analyses of a well-conserved limestone monument surface free of copper showed the almost complete conversion of surface limestone to gypsum. The grey/brown biofilms consisted of actinomycetes and filamentous fungi. The results indicate that copper initially prevents and then enhances limestone deterioration, and that atmospheric pollutants are far less harmful than phototrophic biofilms, since surface areas completely converted to gypsum are well preserved after more than 100 years.

The mineralogical composition of sandstone and its effect on sulphur dioxide deposition

Air pollutants often accelerate stone deterioration in historical buildings and monuments in urban areas. The pollutants are themselves the products of fossil fuel combustion and intensive farming. While this trend seems to have been curbed by strict emission laws in the European Union, in most developing and emerging countries air pollution is an ongoing process due to increasing energy needs and vehicle traffic. Many factors condition natural stone behaviour with respect to gaseous pollutants. Two of the more prominent of such factors are the composition of the atmosphere and the type of stone. Due to their porosity, sandstones are particularly vulnerable to air pollutant attack. Many of the reactions between non-carbonaceous sandstones and these gases are not well understood, however. The present study aimed to acquire an understanding of the processes and factors governing sandstone behaviour when exposed to sulphur dioxide. Seven different sandstones from southern and eastern Germany were analyzed for the study. The binder composition of the stones varied significantly. They also exhibited completely different behaviour in connection with SO2 sorption. Interestingly, while the amount of SO2 deposited was unrelated to the specific surface area of the sandstones, this parameter was closely correlated to the iron oxide content. Iron oxide phases are believed to act as a catalyst in the oxidation of SO2 to SO3. The type and amount of clay mineral, in turn, was found to have no significant impact on initial SO2 deposition in sandstones.

Weathering of limestone building material by mixed sulfate solutions. Characterization of stone microstructure, reaction products and decay forms

This paper presents a multidisciplinary approach to characterize, at both micro- and macro-scales, the behavior of a limestone widely used as construction material in South Spain when interacting with single- and mixed sulfate solutions of differing concentrations. A salt crystallization test that depicts the reality occurring in bottom walls of buildings was used to establish the related decay morphologies and weathering mechanisms. A systematic chemical, mineralogical, petrographic and porosimetric analysis of the fresh and weathered stones, the crystallized salts, and the evolution of ion concentrations of the solutions was performed. Factors controlling the type of fluid transport within the stone and its eventual breakdown were investigated and discussed. Concentrated solutions caused the most intense damage through chemical weathering and crystallization of salts causing a disrupting effect. Simple solutions caused more salt damage than did mixed solutions. This information will enable long-term predictions of material behavior and stone deterioration in buildings.

Stone deterioration and conservation of the ancient Egyptian tomb of Neferhotep (TT 49) in Thebes (Egypt)

Stone deterioration and conservation of the ancient Egyptian tomb of Neferhotep (TT 49) in Thebes (Egypt)

The Influence of Past Protective Treatments on the Deterioration of Historic Stone Façades A Case Study

During a 2002 cleaning operation on the Royal Palace (Madrid, Spain), some stains actually became much more visible after the limestone and granite stones were cleaned. These stains were analysed by several instrumental techniques (both in situ and in the laboratory) and were found to result from past protective treatments. Some of these treatments had formed thin, impermeable films that did not allow the water inside the ashlar to evaporate. Sub- and crypto-efflorescences (gypsum, thenardite and nitratite) broke the protective film, generating efflorescences on the surface. The treatments had not penetrated the stone, and the stains were merely superficial. The method used for the cleaning of the stone façades (pressure water jet) was ineffective for the removal of these protective treatments, which at present are deteriorating the stone on which they were applied.

Controls on permeability: implications for stone weathering

Abstract In the light of a well-researched relationship between rock properties and susceptibility of stone to weathering, the role of permeability in weathering is examined. A review of weathering studies indicates the varied use and nature of porosity data, but the paucity of permeability studies in weathering trials. Key factors that control porosity and permeability, depositional characteristics and diagenetic processes are discussed and investigated, with a view to discussing the implications for stone weathering. Results from experimental studies on a range of rock types comprising sandstone, limestone and granite are presented. The relevance of permeability measurement is explored in terms of spatial mapping and quantitative assessment of the deterioration of natural building stone. Increased knowledge and appreciation of the inherited characteristics of a rock is demonstrated to provide valuable insight and a greater understanding of how natural stone heterogeneity is accentuated and exploited by weathering and continued exposure to moisture and salts. Mapping the spatial distribution of permeability provides greater insight into the extent of variability in stone deterioration and presents the possibility of monitoring and predicting the hydraulic properties of stone and how these are modified by weathering processes.

Review of Digital Image Analysis of Petrographic Thin Sections in Conservation Research

This paper reviews published conservation research that utilizes digital image analysis of petrographic thin sections. Examples involve quantifying quartz microcrack patterns to analyze stone deterioration, conducting porosimetric studies of stone, examining grain-size distribution and grain shape in stone, comprehensively evaluating deterioration mechanisms of stone, studying conservation treatments of stone, characterizing cementitious materials, analyzing ceramic materials, and measuring layer thickness on a variety of materials. Background issues that must be understood before undertaking or evaluating image analysis include experimental design and statistical validity, calibration, image quality, and image enhancement (preprocessing of images). Early work often required in-house computer programs; recent studies make use of new comprehensive image analysis packages. With the emergence of these packages that provide fast preprocessing and measurement of a wide range parameters, we can expect increasing use of image analysis of petrographic thin sections as an analytical tool in the future.

Origin of salts in stone monument degradation using sulphur and oxygen isotopes: First results of the Bourges cathedral (France)

The crystallisation of soluble sulphate salts is one of the most important factors of stone monument degradation. The origin of these salts is variable: marine, air pollution, building or restoration material. The lack of certainty about these sources represents a problem for restoration campaigns. The use of sulphur and oxygen isotopic tracers allows to discriminate the origins of materials and some stone deterioration patterns like black crusts (e.g. [Šrámek J., 1988. Sulfur Isotopes in the revealing corrosion mechanism of stones. 6th International Congress on Deterioration and Conservation of Stone,. Proceedings, ed. J. Ciabach. Nicholas Copernicus University, Torun, Poland, 341–345.]). First results obtained on the Bourges cathedral (France) show that the sulphur and oxygen isotopic composition of sulphates from external (atmospheric pollution) and internal (mortars, plasters and sulphates coming from stone sulphide oxidation) origins constitute well differentiated poles. The isotopic composition of sulphates implied in different stone deterioration patterns is well explained by a combination of these poles. The present study will be extended to other French monuments located in different lithological and hydroclimatic settings where contributions of sea salts and ancient chemical treatments are suspected.

Microbial Deterioration of Historic Stone

Microbial Deterioration of Historic Stone

Measurement of limestone biodeterioration using the Ca 2+ binding fluorochrome Rhod-5N

Limestone and marble have been used extensively in the construction of modern and historic buildings. Microbial colonization and growth on these stone structures is common. Microbial deterioration of stone has been assessed by measuring Ca 2+ released from the stone, using ion selective electrodes and titration with EDTA. In this study, the calcium binding fluorochrome Rhod-5N was used to measure Ca 2+ released from limestone by endolithic bacteria as an indicator of biodeterioration. In a 17 d flask experiment, Ca 2+ released by endolithic bacteria was twice that of uninoculated controls. Rhod-5N is a rapid and accurate method for measuring microbial biodeterioration of stone.

Erosion of limestone building surfaces caused by wind-driven rain: 2. Numerical modeling

Wind-driven rain and its effect on surface stone deterioration have been studied at the Cathedral of Learning, a tall limestone building on the University of Pittsburgh campus. In this second paper of the series, a numerical method based on computational fluid dynamics techniques is used to predict wind-driven rain on the Cathedral. Three steps are involved: computing the airflow field around the building, determining raindrop trajectories, and estimating total rain impingement based on meteorological data. Results are expressed in terms of the Catch Ratio, the flux of rain on the building walls divided by the flux of rain on the ground. The method is applied to 94 rain events during the measurement period. Results show good agreement with field data, indicating that the method can provide reasonable predictions of wind-driven rain.

Study of the deterioration of sandstone due to acid rain and humid SO2 gas

AbstractThe aim of this work was to study the deterioration of various kinds of sandstone due to acid rain and SO2 gas. The samples were taken from three quarries in Poland and one sample was from a tomb about 100 years old. To elucidate the mechanism of stone deterioration, simple experiments were performed. The sandstone samples were immersed for several weeks in SO2 aqueous solution of pH ≈ 4. Similar experiments were performed using SO2 aqueous solution of pH ≈ 1.5. The concentrations of Ca, Mg and Fe leached from the sandstone samples were measured with TXRF. An additional experiment was carried out with the use of radioactive 35SO2. The samples were exposed to both 35SO2 aqueous solution and to 35SO2 gas. The autoradiograms obtained from the sample cross‐sections indicated that sulfur penetrated to the interior parts of sandstone samples, especially from SO2 gas. Copyright © 2004 John Wiley & Sons, Ltd.

Partial reburial of West Ruin at Aztec Ruins National Monument

Aztec Ruins National Monument is a World Heritage Site in northwestern New Mexico, USA. More than 50,000 visitors come to the site each year, specifically to visit West Ruin, a 12th–13th century, multi-storey Ancestral Pueblo an (Anasazi) village with over 400 rooms. West Ruin was excavated in the early 1900s and was intentionally left exposed for public access and interpretation. The walls, constructed of shaped sandstone blocks set in mud mortar, have gradually deteriorated, despite years of stabilization and preservation efforts. In 1999, park management began to partially rebury portions of West Ruin as a reversible long-term preservation treatment. While partial reburial allows for presentation of the site to visitors, it also results in uneven fill levels in many rooms. Differential fill levels can increase the area subject to migration and capillary rise of moisture through the walls, and can accelerate stone and mortar deterioration on the exposed wall faces. Differential fill levels can also lead to structural instability from unequal pressure exerted between filled and non-filled areas. To mitigate moisture migration and structural instability from differential fills, a soil retention system was designed and tested using layers of synthetic three-dimensional earth confinement cells. This paper discusses the design and implementation of the soil retention system within the larger context of a multi-phased reburial project underway at Aztec Ruins National Monument.

Characterization, water transfer properties and deterioration in tuffeau: building material in the Loire valley—France

Water plays a fundamental role in the phenomena of stone deterioration. A highly porous limestone called tuffeau used in the Loire castles in France is characterized. Several techniques for pore space investigation and anisotropy determination are presented and their range of application is discussed. Water retention and transfer properties related to the pore space characteristics are determined as a function of relative humidity. The experimental set-up and tests presented have been chosen for their simple execution and interesting data produced for both fresh and deteriorated stone.

Salt-induced decay in calcareous stone monuments and buildings in a marine environment in SW France

Salt weathering can be a hazard with significant cultural and economic implications. Salt-induced deterioration of architectural heritage is considered to be accelerated drastically in marine environments. This article investigates the weathering mechanisms and weathering forms in two calcareous stone types used in monuments and buildings on the SW coast of France. The mineralogical, chemical, textural and pore-system characteristics of freshly quarried and decayed stones from quarry, monuments and buildings were determined, and salts loading identified. The stones’ resistance against salt weathering was estimated by comparing calculated crystallisation pressures, which are function of the pore size distribution, with the tensile strengths measured by Auger [Alteration des roches sous influence marine; degradation des pierres en oeuvre et simulation acceleree en laboratoir. These Doctorat d'Etat es Siences. Universite de Poitiers, France (1987)]. Results show that Crazannes sparite and La Pallice micrite behave differently with respect to water and salt-spray absorption and local salt precipitation since their pore networks, which control hydric properties, are different. Therefore, diverse weathering patterns due to salt crystallisation pressures were identified in the stones as influenced largely by their pore size distribution: alveolar weathering and granular disintegration in the sparite vs. flaking and micro-fissuring in the micrite. These mechanisms operate in response to salt inputs from a variety of sources—mainly marine aerosols and atmospheric pollution—as corroborated by the so-called enrichment factors (EFs). Wind is believed to trigger alveolar weathering in the heterogeneous sparite. Short-term observations in La Pallice micrite show rapid salt-induced breakdown through ‘fatigue’ effects. Determining factors involved in stone deterioration is important in the design of proper interventions for protecting historic buildings.

Acid deposition and the deterioration of stone: a brief review of a broad topic

Abstract The causes of stone deterioration due to acid deposition are examined, with specific reference made to important research on this subject from the past thirty years. The major topics covered include: dry deposition of atmospheric pollutants, the primary agent of acid deterioration of stone in urban areas; wet deposition, commonly referred to as acid rain; and major deterioration mechanisms. Key factors are dry deposition of gaseous pollutants such as SO 2 and NOx, the nature of the stone, including texture and porosity, and the presence of moisture on its surface as well as the ‘time of wetness’.

Implications of future climate change for stone deterioration

Abstract Climate change over the next 100 years is likely to have a range of direct and indirect impacts on many natural and physical environments, including the built environment. Important influences on the built environment will include alterations in temperature, precipitation, extreme climatic events, soil conditions, groundwater and sea level. Some processes of building stone decay will be accelerated or worsened by climate change, whilst others will be retarded. The impacts on individual processes can be conceptualized, but it is difficult to assess or quantify the overall risk posed by climate change given currently available data. Linking global-scale changes to the response of individual walls or buildings remains a challenge. Overall changes in decay rates could also be related to climatic change. As an example downscaled climate predictions, knowledge of stock at risk and long-term decay rates can be used to assess the future of building stone decay in the UK. Using the UK Climatic Impacts Programme’s (UKCIP98) regional climate change projections an increasing NW-SE climatic gradient is predicted, which should enhance chemical weathering of silicate building materials in the NW and increase crystallization damage of limestones in the SE.