Conservation and Restoration of Historic Mortars and Masonry Structures

Most of today’s Austria was part of the alpine province of Noricum, formally incorporated into the Roman Empire in the first century C.E. As trade flourished the area was quickly Romanized and this is reflected by surviving wall paintings exhibiting high proficiency in painting and plastering technique and utilizing precious and rare pigments.This contribution examines the differences that can be found in roughly contemporaneous Roman wall paintings from Noricum. In the context of an ongoing study of Roman pigments, the chemical profile of the top paint layers of plaster fragments in museum collections that displayed monochrome and large-scale application of commonly available Egyptian Blue and expensive Cinnabar/Vermillion were analysed semi-quantitatively by portable XRF. Then stratigraphic cross sections of wall painting samples were made from a selection of plaster fragments that included every plaster preparation layer down to the arriccio. These were examined by light microscopy, SEM/EDX and digital image analysis. Through this process, this study intended to determine if there is a correlation between changes in pigment production and painting and plastering technique.These methods were able to reveal the technical differences in how wall paintings were prepared and how pigments were used in different ways at several Roman sites of Noricum. The sites closer to Italia province showed artisanship more closely resembling that used in the central Empire, while those further north evolved a unique style. This finding reflects trade routes and the development of regional techniques in the Alpine area.

On the Maltese Islands, architectural decoration in historic buildings is widely made of the local Lower Globigerina Limestone, a soft porous stone easy to carve. Little is known, on the other hand, about plaster reliefs (or ‘stuccos’), particularly from a technological point of view. The present study focuses on a plaster relief found in the Baroque Argotti Villa, located in the historic Argotti Botanic Gardens (Floriana, Malta), the layout of which dates back to the period of the Knights of St John in Malta (1530–1798). The relief, Baroque in style and featuring a rope motif and scallop shells, shows the presence of three main plaster layers, and several overlapping paint layers. Remains of painted plaster above the relief and on the dado suggest the possible presence of a past wider decorative scheme. Examination on-site was complemented with analyses of samples taken from the relief. Cross- and thin sections were analysed under a Polarized Light Microscope (PLM) and a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray Analysis (EDX). The plasters are composed of carbonated lime as the binder. Mainly carbonatic aggregates are present (possibly from local Maltese limestone, showing fossils), but also gypsum aggregates and to a much lower extent silicate-aluminate aggregates.

Two types of air lime mortars with inclusion of sesame cooking oil were synthesized. The behavior of mortars in the site conditions and the laboratory can be distinct. Hence, the mortars were cured in two laboratory and natural climatic conditions of and Persepolis World Heritage Site. The mortars were monitored for two years under both conditions and the results demonstrated distinctions in characteristics of mortars, emanating from curing conditions. The air lime mortars cured in the site conditions exhibited increment in durability and hydric properties. In the natural outdoor conditions, some effects of addition of organics to mortars, such as retarding their setting time were less highlighted compared to laboratory curing mortars.

The hydraulic features of lime-based mortars are primarily determined by the occurrence in the raw materials of variable amounts of reactive silica (SiO2) and alumina (Al2O3) that, in presence of water, interact with lime (CaO) to form different hydrated products (C-A-H; C-A-S-H; C-S-H). Under certain conditions, other hydrated products, based on the interaction of magnesium with silica (and sometimes also with alumina) can occur (M-S-H/M-A-S-H). The target of this research is the analysis and comparison of the characteristics and structure of calcium-based silico/aluminate hydrates and magnesium-based silico/aluminate hydrates in ancient mortars and concretes. We adopted a multianalytical approach, involving Optical Microscopy (OM), X-Ray powder diffraction (XRPD), scanning electron microscopy and energy-dispersive microanalysis (SEM-EDS) and magic-angle spinning solid-state nuclear magnetic resonance (MAS-SS NMR), for characterizing samples with different composition and structural function from the sites of Aquileia (Northern Italy), Nora (Sardinia) and Pompeii (Naples). The results we obtained demonstrate the occurrence of different hydraulic phases in the mortar-based materials, whose development primarily depends on the array of raw materials used in the manufacturing of the compounds. However, the observed hydraulic phases present a prevalent gel-like structure, that was not adequately parametrized and quantified adopting the analytical approach traditionally employed for the characterization of ancient mortars (i.e. OM, XRPD, SEM-EDS). In this perspective, the utilization of MAS-SS NMR resulted crucial in characterizing the chemical environment of hydraulic phases, and C-S-H in particular, by discriminating the degree of polymerization of the silicate tetrahedra even in disordered structures.

The Venetian Arsenals of Chania in southern Greece constitute an important monument of cultural and industrial heritage, as well as a key landmark for the town. In the framework of the holistic study for the restoration of the building, mortars, plasters, and stones were sampled and analyzed in order to identify the construction phases and evaluate the decay state of the materials. Open porosity, bulk density and soluble salts were measured. Additionally, the mortars were chemically and mineralogically characterized through X-ray fluorescence analysis (XRF), infrared spectroscopy (FTIR), differential thermogravimetric analysis (DTA/TG) and X-Ray diffraction (XRD) to identify the mortars’ technology and the composition of the raw materials. Furthermore, the granulometric analysis and the optical microscopy provided information about the aggregates and the consistency of the mortars. The original Venetian mortars exceebited good consistency and excellent coherence with the building stones. The Ottoman mortars, on the contrary, due to their poor consistency, have suffered the greatest decay. This research constitutes the base for the design of compatible restoration materials, thus ensuring the sustainable performance of the monument.

The growing interest in preserving the built heritage is a driving force towards the search for new rehabilitation solutions compatible with the original construction techniques of ancient buildings. For the design of an adequate reinforcement solution, it is necessary to know in detail the building to be rehabilitated, as well as its original constructive solutions and materials.This paper presents the results of an experimental campaign on samples of air lime-based laying and coating mortars, extracted from an old masonry building in the historic center of Lisbon, built in 1910, during the rehabilitation works. The different parameters analyzed allow for the composition characterization and evaluation of their mechanical, physical and chemical properties. Based on this characterization, the influence of these mortars on the overall behavior of load-bearing walls of buildings belonging to the typology under study is also evaluated.Considering the results obtained in the characterization tests for the mortars in study, it was verified that the binder used in both mortars was air lime. The values for compressive strength, modulus of elasticity and the curves obtained in the capillarity and drying tests, are also compatible with this type of mortars. It was determined that the mortars are similar in terms of physical and mechanical characteristics, to Portuguese mortars studied in current buildings of the same historical period. This type of information is crucial in a structural analysis and allows to identify materials compatible with the original ones that can be used in rehabilitation interventions.

The Baths of Porta Marina were an imperial public complex located in the maritime suburban district of Ostia, the city harbor of Rome. During its large period of use from the 2nd century AD until the 6th century AD, several modifications of capacity and thermal path took place, resulting in architectural modifications. Previous studies based on archaeological evidence, written sources, architectural and stratigraphic analyses have provided thorough chronological data for construction phases. Characterization of hydraulic coatings and bedding mortars has been carried out focusing on waterproofing processes of antique hydraulic facilities and to propose a timeline of raw materials uses for this particular building and for others hydraulic facilities preceding the thermal complex (1st century AD). Mineralogical, chemical, and petrographic analyses were performed on several mortar samples from pools and cisterns from different construction phases of the Baths of Porta Marina. They confirm that mortars of Roman waterproof coverings, made with pozzolanic aggregates, show a persistent composition over centuries, hardly distinguishable macroscopically. Nonetheless, petrographic examination has been an interesting tool to highlight differences among the mortars. Some distinctive features of volcanic aggregates allow us to identify different depositional units from Alban Hills volcanic district as sources.

The exterior coatings of old buildings were mostly made with lime-based mortars. As coverings for the external facades of buildings, they are elements that are highly exposed to several actions such as climate actions, mechanical actions, etc., and therefore, they are the first ones to need conservation, rehabilitation or replacement interventions.The conservation, rehabilitation or replacement of lime-based coatings are actions that involve the complicated task of choosing a new mortar that should not only be compatible with the existing mortar, but also compatible with the substrate itself.There are two possible ways to properly choose the mortar to use, whether you choose to reproduce the old mortar, thus seeking to ensure its compatibility and its proper functioning, or you formulate a compatible mortar with an adequate behavior for the building in question, with an appearance that preserves the building's image.In practice, the first way is impossible on its own as it is not yet possible to accurately determine the “evolution” of the mortar (dynamic processes in constant evolution – crystallization, dissolution and recrystallization, etc.) and it is also difficult to identify the technologies used in its execution and application and we are also unaware of the climatic conditions that may have influenced the curing process. The ideal will be a process involving the two mentioned ways.For this, the first task should be to know the characteristics of the existing mortars and then select a similar mortar with an adequate behavior for the building.What is presented in this work is a campaign carried out in order to choose replacement mortars for several old buildings located in the center of Portugal. For this, the existing mortars were characterized, suitable replacement mortars were selected and applied to the existing buildings. After they had been cured, an in situ experimental campaign was carried out in order to assess the suitability of the chosen mortars for the walls of the buildings.

The “Terranova” render was a ready-mix dry colored mortar which diffused in Europe in the first half of the XX Century. During the 1920s and 1930s, it was largely adopted in Italy as a finishing solution for the façades of rationalist architecture. It quickly became very popular thanks to its excellent aspect and high durability. Despite its wide diffusion, its formulation and technical properties remain basically unknown, also due to some patents protecting it. For this reason, Terranova renders are often not recognized in restoration interventions. In this study, different samples of supposedly Terranova render were collected from three rationalist buildings in Ferrara and Forlì (Italy) dating back to the Thirties and a thorough characterization was carried out to investigate their formulations and features. A comparison was also made with a Terranova sample collected from a rationalist building in Bologna (Italy), analysed in a previous study. The aim was to characterize this material and disclose, if existing, a recurrent formulation, to explain its outstanding properties and advance the design of compatible repair mortars. Despite the recurrence of some features, defining a common formulation seemed to be hard, suggesting that alternative recipes were used in manufacturing this industrial render.

Study models of buildings’ degradation allow the estimation of their service life, assisting in planning their maintenance. However, determining an accurate method of applying these study models may be challenging, since there are unknown variables involved, such as the materials and construction techniques, besides interventions and environmental factors that impacted the building along the years. In historic buildings, it is difficult to know the mechanisms of deterioration, and to obtain reliable information about each building. The facade of historic buildings ends up being a great source of information though, since it is the building’s element most exposed to degradation. Therefore, studying the deterioration of external mortar coatings of historic buildings may improve the quality of the information about them, and ensure heritage preservation. This paper discusses different methods used to study the service life of building elements and presents a review of mathematical models developed that not yet been directly applied to study the degradation of facades of historic buildings, identifying the main variables used, and indicating which model would be the best suited for applied in external mortar cladding in historical buildings.

A number of military fortresses built between 1853 and 1914 by the Austrian‐Hungarian Empire in today’s Republic of Montenegro have been investigated by the Austrian Archaeological Institute. The ongoing survey first focused on three sites dating between 1858 and 1897. Mortars had been diversely used in all of them for different purposes of construction.Analyses were performed on mortar samples by thin-section microscopy and SEM. The results reveal use of several lime, natural “Roman” cement and Portland cement materials, depending on their application in the building and on the period of construction. All three fort buildings contain mainly air lime mortars as bedding and filling of the stone masonry, while pointing on exterior walls and tamped concretes are usually based on Portland cements. The microscopic features of the Portland cement (PC) clinkers reflect the typical conditions of early PC production. Roman cement (RC) mortars were only occasionally found.Our contribution includes a presentation of the fortresses and their construction principles, followed by a discussion of the mortars by their binder constituents and aggregates. In the context of the state of the Austro-Hungarian cement industry in the 19th century, the observations reveal one of the earliest applications of Portland cement in the whole Empire.

Limewashes have been used as finishing coats for walls since ancient times. Its protective, aesthetic, antiseptic properties and cost-efficiency are the ground for its worldwide application. The main drawback of lime-based paints is their low durability towards the action of water, particularly wind-driven rain. Additives that grant water-repellent properties have been added to these paints to overcome this issue. Among these additives, vegetable oils have been reported worldwide in ancient documents. In this work, three vegetable oils have been selected based on their composition and promising results in previous studies, global availability, and cost-efficiency: rapeseed, sunflower, and sunflower oil with high oleic acid content. Additionally, a commercial water-repellent lime putty with the addition of olive oil was included to prepare a limewash and compare it with the lab-prepared paints. Two types of stone with very different porous structures were used as substrates to compare the effect of the paints on their water transport properties. The substrate with higher porosity and wider pores showed promising results in terms of water-repellence and drying. In contrast, the stone with lower porosity and fine pores did not show good results. Based on this study, suggestions for further research to improve the performance of the paints in substrates with low porosity and narrow pore size distribution are given.

This study investigated the characterization of lime collected from the tomb of Songje-ri in Naju, Republic of Korea. The site is highly significant to understand the burial culture of ancient period in Korean history. The lime remained partially on the wall inside the tomb. The mineralogical and chemical properties of lime samples were characterized by digital microscope, X-ray diffraction analysis (XRD), thermal analysis (TG-DSC), X-ray fluorescence analysis (XRF) and mercury intrusion porosimetry (MIP). As a result of analysis, the sample is a plaster consisting only of lime, which was manufactured by shells. Traces of a small amount of organic matter are confirmed, but further study is required for artificial addition.

The archaeological sites of Mikulčice and Pohansko (South Moravia – the Czech Republic) belong to the oldest and the most important localities of Slavic settlement in Central Europe. A number of historic mortars sampled here were collected in order to study their composition, mortar structural characteristics and raw materials provenance. The aim of this study was not only the comparison and characterisation of the historical mortars from these archaeological sites, but we also evaluated the suitability of these mortars to be dated by 14C analysis.The samples were characterised by several analytical techniques as polarised light and scanning electron microscopy, thermal analyses or quantitative X-ray diffraction. Stable isotope analyses and cathodoluminescence were also performed. The collected mortars contained a considerable amount of lime particles that can adversely affect the possibility of 14C radiocarbon dating. According to the results of the analyses, the samples from both localities had a similar character. Mortars were very rich in the binder and contained unburnt limestone fragments that occurred frequently. Unburnt fragments were classified mostly as a micritic limestone contained bioclastic fragments. This material was determined as Ernstbrunn limestones according to the composition and structure. Stable isotope analysis also suggested that all studied lime samples came from a single source. The presence of geogenic carbonates (not fully burnt lime) affects the resulting 14C age of the analysed samples fundamentally. The character of mortars leads to a discussion on how to adapt the separating procedures of the individual fractions and avoid geogenic carbon contamination.

Sgraffito technique was used to decorate renders by scratching the top layer of lime wash in the Renaissance time. In order to contribute to the preservation of surviving sgraffiti in the town of Slavonice in the Czech Republic a study was carried out assessing the possibility to replicate the original materials and the application techniques. Historical sgraffito layers were sampled in situ and studied in a laboratory by commonly used analytical methods - OM, TA, XRD, SEM-EDS. The raw materials, lime binder and sand, were characterised and the mixing proportion app. 1 to 0.7 (vol.) of lime putty to sand was determined. Based on the character of the local limestone, a similar raw material was obtained and burnt in an experimental lime kiln. The sand was obtained locally from a disused pit quarry. Obtaining the raw materials from similar sources as the historic ones allowed studying possible production technologies and application techniques. Appropriate and probable techniques were verified by a series of practical experiments. These considered: lime putty v. dry slaked hydrate; thickness of a layer; trowelling and final finishing; timing of drawing, scratching application of lime wash. The performance of the produced mortar mix was assessed by compressive and flexural strengths, capillary absorption, drying index, open porosity and water vapour diffusion coefficient. The mortar, designed as a material replica of the original, was used in a conservation project on a façade of a house, where missing parts of a sgraffito render were reconstructed.

Earth mortars and gypsum mortars present ecological advantages compared to mortars made with other common binders. When applied as plasters, they are also referred as having advantages in improving comfort and indoor air quality. For earth plasters, this improvement is associated with the hygroscopic capacity of the clay minerals, which promotes high sorption and desorption capacity of water vapor. So, earth plasters can contribute to the regulation of the indoor relative humidity. Another important advantage of plasters could be their ability to capture carbon dioxide (CO2). In the present study, the sorption and desorption performance, and the capacity to capture CO2 by earth and gypsum plasters are evaluated. It is confirmed that the earth plaster has the greatest sorption and desorption capacity, but also higher CO2 capture capacity than gypsum plaster. This confirmation opens new perspectives for the use of functionalized plasters that guarantee greater control of air quality inside buildings.

It is increasingly necessary to rethink constructive solutions to minimize the construction industry’s environmental impact without compromising technical characteristics, including conservation. The replacement of natural sand by ceramic waste and clayish earth was analyzed in the fresh and hardened state of earth and air lime mortars. Seven different mortars with clayish earth and air lime as binders were produced and characterized: two earth mortars with added sand and with brick waste instead of sand; five air lime mortars with sand, with clayish earth, or with brick waste instead of sand. The replacement of sand by brick waste promotes a decrease in the mortars’ dry bulk density and mechanical strengths. For the air lime mortar, the replacement of sand by brick waste promotes an increase in dynamic modulus of elasticity, compared with the reference mortar with low flow. The air lime mortar with clayish earth presents lower flexural strength and dynamic modulus of elasticity. Many of the mortars with alternative added aggregate fulfil the requirements for plastering old and new buildings and, based on old practices, can be a more sustainable alternative with natural pigmentation. However, training is needed for professionals using this type of mortars.

The need to develop products for the conservation of the architectural heritage, in particular binders for plasters, is increased nowadays and those products are required to be in line with green production system and materials in full compliance with current environmental sustainability criteria. It has already been established that Natural Hydraulic Lime (NHL) is a good material for restoration; it is compatible with ancient materials and respects the environmental requirements. The use of green technologies often involves the partial use of environmental low impact materials that do not always find practical use in restoration. The starting point of the research is the selection and study of NHL-based commercial plasters used for the conservation of historic masonries and their optimization through additives cement-free in order to create green products for applications in the conservative restoration of historical heritage. The five different types of formulations chosen for this work, has been evaluated and analyzed from a physical and mechanical point of view, through dynamic elastic module, compression and flexion tests, porosity and density analysis. During the execution of the research, the focus was on the effect of microstructural features of porous material, investigated in laboratory with porosimetry test as they are fundamental parameters for studying compatibility with pre-existing materials and durability over time.

The Mirante da Quinta da Azeda, in Setúbal (Portugal), is a peculiar observation tower built in the early 20th century, and one of the first examples in which reinforced concrete was applied in Portugal. It has an unusual architectural configuration, displaying elements of great slenderness. In the scope of the CemRestore research project - Mortars for the conservation of early 20th century buildings: compatibility and sustainability, several mortar and concrete samples were collected from this structure and were characterized using a combination of mineralogical, microstructural, physical, and mechanical techniques, including XRD, petrography, SEM-EDS, open porosity, capillarity coefficient, compressive strength, and ultrasonic pulse testing. In this paper, the main characterization results are presented and discussed. The results show that all structural and decorative samples are made with Portland cement, while one rendering mortar is lime-based. The sand is mostly siliceous whereas pebbles and crushed limestone can be found as coarse aggregates in concrete samples. This characterization allows for broadening the scientific knowledge about the materials of that period used in Portugal, also enabling the establishment of the requirements to be met by mortars and concrete to be used in the repair of this distinct structure.

Traditional stone aggregates used to prepare mortars are generally considered inert fillers that do not interact with a binder. The European Green Deal, on the other hand, encourages the use of secondary material as aggregate. This secondary material is rarely an inert part of lime-based composites. This study focuses on heavy metal contaminated aggregate, for which has already been confirmed to alter microstructure development and lower the early strength of cement composites. Its influence on the early age properties of hydraulic lime mortar was studied through microstructure development recorded using transmission ultrasound technique and tensile and compressive strength after 1, 3 and 7 days. Results are then compared to those of cement composites. The obtained results show that heavy metals delay microstructure development of hydraulic lime mixture during the first 60 h, but do not decrease the tensile and compressive strength of the mortar after 3 and 7 days, as is the case with cement mortar.

Gaji is the Georgian name both for a gypsum-and-clay-containing soft rock found in eastern Georgia, and for the plaster traditionally derived from it. Gypsum-earth plasters have a long history of use across Caucasia, central Asia, and the Middle East. Gaji has been used in the preparation of mortars, plasters and decorative finishes, and as a support for Georgian religious and secular wall paintings together spanning the 9th – 20th centuries. Little research has been conducted into its properties, however, and within the context of wall painting conservation neither its influence on condition nor its implications for treatment have been adequately explored. Using the Church of St. Demetrios of Thessaloniki, rediscovered in 2015, at the monastic complex of David Gareji as an example, this paper explores the use of gaji plaster technology and the conservation challenges it presents.

The development of reinforced concrete through the 20th century has resulted in a wealth of culturally significant concrete structures around the world. However, as a relatively modern material durability issues were not fully understood at the time of construction, and many of these structures require ongoing interventions as a result. While there is now a general acceptance of the importance of concrete heritage from this era, there few widely accepted guidelines on the approach to its preservation and conservation. In particular, despite many studies and published guidance on concrete repair and the performance of concrete repairs, there are few on the long-term performance of patch repairs designed to match the aesthetic of the original while simultaneously keeping loss of the original fabric to a minimum. As a response to this challenge, three institutions, the Getty Conservation Institute (GCI), Historic England (HE) and Laboratoire de Recherche des Monuments Historiques (LRMH) are collaborating on The Performance Evaluation of Patch Repairs on Historic Concrete Structures (PEPS) to produce practical guidance that will help those repairing historic concrete. This paper provides an overview of the assessment methodology that has been developed as part of this international collaboration.

The rise of cement at the beginning of the XX century provoked the lime mortars decay. In the case of Spain, they were revival after the Spanish Civil War (1936–1939) due to the insolation of the country (autarky period). It is especially interesting since traditional materials defined new styles. An example of this duality is the Obra Sindical del Hogar (OSH) pavilion, at Casa de Campo exhibition area in Madrid. The ceramic wall placed on its entrance is a perfect example of modernity in the graphical representation of the scenes, using traditional techniques and materials: porous ceramic and lime mortars. As part of the restoration of this mural, a complete analysis of the original mortars and ceramic had been performed. The results showed a careful selection of the materials and the knowledge of the workforces. Porous ceramic calcined at low temperature as support of the glassy treatment and their compatibility with the aerial lime mortar defined its state of conservation, in spite of the abandon suffered for more than 40 years. Air lime mortars showed a high compactness and a reduced porosity mainly because a careful selection of the aggregates and care in their execution and installation.

Using laboratory produced mortar samples in wall painting conservation research requires sufficient chemical and physical resemblance to the original object to make the tests on the samples relevant. This study applies the contact sponge method comparing the water absorption rate of limewashed medieval wall painting plaster with mortar samples of varying binder-to-aggregate ratios produced by the hot-mix technique and with lime putty mortar. Different types of limewashes are also examined. Based on this comparison, the study evaluates the samples’ suitability as models for wall painting conservation research. Moreover, the study explores the validity of the contact sponge method for measuring highly porous mortars.The experiment demonstrates that the contact sponge method can be used for measuring the water absorption rate of highly porous mortar samples, and that the fastest water absorption rates are found in the mortar samples with the highest lime content. Moreover, the closer the sample’s binder-to-aggregate ratio is to the historical plaster, the more similar the values are. The poorest correlations are found for lime putty mortar samples with a 1:3 ratio heretofore used in conservation trials. Furthermore, the absorption rate is significantly influenced by the type of limewash on the samples.

Križanke Outdoor Theatre is a theatre in Ljubljana, Slovenia, used for summer festivals. Between 1952 and 1956, architect Jože Plečnik converted this former monastery into one of the city’s most important cultural venues. To the left of the entrance to the courtyard is a small triumphal arch decorated with sgraffito. The conservation and restoration of the triumphal arch was carried out in the summer of 2021. During the investigation of the historical documentation and the first steps of surface cleaning, it was found that there had been an intervention in the past. Microscopic analysis revealed that a lime-cement mortar with aggregates consisting mainly of round carbonate grains had been used for the triumphal arch. The original and the reconstructed sgraffito plaster consisted of pigmented lime binder. The black pigment in the grey plaster was identified as carbon black. Pigments such as iron oxide (hematite) and iron hydroxide (goethite) with some carbon black are present in the red coloured plaster of the original sgraffito. Only hematite was used for the reconstructed red coloured sgraffito plaster. The mineralogical-petrographic composition of the aggregates in the two (original and reconstructed) sgraffito plasters is similar and consists mainly of carbonate grains. On the surface of the original sgraffito plaster there was a gypsum layer as a weathering product. The goal of this research was to study and characterise the plasters used in sgraffito decoration. The information was crucial for processes such as the development of repair plasters for the damaged parts.

Sodium chloride (NaCl) is one of the most commonly occurring weathering agents, responsible for a progressive damage in mortar. Current solutions to mitigate salt damage in mortar, such as the use of mixed-in water repellent additives, have often exhibited low compatibility with the existing building fabric. In the last years, research has shown promising results in mitigating salt decay by making use of crystallisation inhibitors. Sodium ferrocyanide is one of the inhibitors that has proven to be particularly effective to reduce damage due to sodium chloride crystallisation.In this research the possibility of developing hydraulic mortars with mixed-in inhibitor (sodium ferrocyanide) for an improved resistance to sodium chloride crystallisation damage is investigated. As a first step, the interaction between the inhibitor and the hydraulic binder: natural hydraulic lime (NHL), was studied; the results are presented in this paper. Various concentrations of sodium ferrocyanide were tested (0%, 0.1% and 1% by binder weight). The effect of the inhibitor on several physical (hydration, water absorption, pore size distribution) and mechanical (compressive and flexural strength) properties was experimentally assessed, using several complementary methods and techniques. The results show that the addition of the sodium ferrocyanide does not affect the fresh and hardened properties of mortar. These results are promising and open new possibilities for the application of inhibitors to improve the durability of hydraulic mortars.

It is well known that the most effective method to improve the internal tensile strength of lime-based mortar and minimize plastic shrinkage is the incorporation of fibres as reinforcement. Nowadays, commonly used fibres in lime-based mortars are polymeric or synthetic ones, while only recently the building industry’s current trend to develop sustainable materials, brought natural fibres to the forefront. Natural fibres are abundant, low-cost, renewable, with a CO2-neutral life cycle and high filling levels possible, sustainable, energy efficient, biodegradable, non-toxic, of nonabrasive nature, of low weight and density, yielding lightweight composites of low environmental footprint. In this sense, the current research aims to examine the possibility of utilization the solid lignocellulosic waste material generated from the lavender oil extraction plants in lime-based mortars. The lavender fibres were introduced in two ways: as additives in 1.5% b.v. of the mortar and as a layer (net) between two mortar layers. Both techniques were often met in historic structures. Specimens were produced to examine the mechanical, thermal, physical and microstructure characteristics of the composites. The results indicate the utilization potential of aromatic plants’ wastes in the building sector contributing to the development of sustainable and energy efficient materials suitable for repair works.

Reducing greenhouse gas emissions and dependence on fossil fuels is the cornerstone of all European climate and energy strategies. At the same time, waste reduction and recycling are at the top of the European waste hierarchy. Therefore, the European Union (EU) is turning to renewable energy and sustainable options that address complex local conditions and growing energy and material needs. Bioenergy is the most important renewable energy source in the EU, accounting for more than 2/3 of the renewable energy mix. As wood is a carbon neutral energy source, it is one of the predominant sources of biomass for energy production in the EU. However, the continuous expansion of wood biomass power plants leads to the formation of wood biomass ash (WBA), a solid by-product of wood combustion on a large scale. The disposal of WBA is a problem that requires long-term strategic and sustainable solutions. Therefore, WBA is the focus of this paper as an alternative material with pozzolanic and/or hydraulic properties needed for the production of waste-based artificial hydraulic lime (AHL). This type of a novel hybrid WBA-lime binder would serve as an end result for the production of a repair mortar for historical buildings. Two different sources of locally available WBA were considered for the preparation of binders as mixtures of WBA and natural hydraulic lime (NHL) in different ratios. Based on the chemico-mineralogical composition and physical properties, the potential of WBA as a component of an AHL is evaluated. The contribution of the individual binder mixtures to mortar properties was analyzed on the basis of the demonstrated water demand, the flow diameter, and the compressive and flexural strength according to EN 459-1.

Climate change has become the main problems of humanity, affecting all the everyday actions and habits. The decrease of CO2 emissions is mandatory for the protection of the environment and the construction sector has a 36% share of the global problem. On the other hand, conservation of cultural heritage remains one of the main targets in European level. In the case of conservation works, the materials and the techniques used follow specific regulations included in relative norms. The aim of this work is to combine the needs mentioned above for sustainable and qualitative materials that can be used for restoration works. In this frame, the properties (chemical, physical, mineralogical, mechanical) of four perlite by-products were tested and the results were reviewed to meet the criteria set by the regulations which they will determine the possibility to use them in air lime mortar production. Fineness, color, salt content, chemical composition and reactivity were determined. The alumisilicate content of the binders was measured to comply with regulations for natural pozzolans and the pozzolanicity index of the binders was also tested. The research results to the possibility to follow specific criteria to evaluate industrial by-products, saving natural resources and increasing the environmental profile of air lime-based mortars.

Perlite is a volcanic rock containing high amount of amorphous material as well as alumino-silicate minerals. The outcoming product (expanded perlite) is often used in construction, due to its light weight and insulating properties. During its industrial process, an increasing number of by-products results that mainly remains unexploited as the fineness of these materials renders them difficult to store. In this study, an effort has been made to experimentally study the influence of two by-products (D1S, D1C), in lime-based mortars. These materials have been used as binders. To this direction, 9 mortar mixtures where manufactured and tested where natural pozzolan was gradually replaced by the perlite by-products. The Binder/Aggregate ratio in all mixtures was maintained at 1/2, whereas aggregates were natural of siliceous origin and gradation 0–4 mm. The physico-mechanical properties of the specimens were tested at the age of 28 and 90 days. From the correlation of the results, it was asserted that the partial or even total substitution of natural pozzolan by perlite by-products, enhanced the mortars’ physical and mechanical properties. It maybe therefore concluded that the exploitation of waste perlite in the construction sector is feasible, leading to the development of effective, low-cost and environmentally friendly products for specific applications.

The present paper aims at comparing diammonium hydrogen phosphate (DAP) and nanolimes (NL) as consolidants for the preservation of lime mortars. The durability of the two consolidants was evaluated in terms of resistance to freezing thawing and salt crystallization cycles. The results of the study point out that, compared to the untreated reference and NL-treated samples, DAP-treated mortars showed much improved resistance to freezing-thawing cycles. A lower benefit was found in the case of salt crystallization cycles, as DAP-treated samples exhibited a behavior substantially similar to untreated and NL-treated ones. The different improvement in durability observed for the two weathering processes could be ascribed, on the one hand, to the slight modification of the pore size distribution after treatment (which may lead to increased crystallization pressure) and, on the other hand, to the severity of the salt weathering test (involving the use of a saturated Na2SO4·10H2O solution). All things considered, the potential of the DAP treatment for the conservation of lime-based mortars is confirmed.

This paper presents a study on partial replacement of lime binder with fine spongilite with the purpose of exploring a new application of this natural material as lime mortar additive. Standard air lime mortars were made by incorporating from 0% to 40% of spongilite powder in replacement to lime and their mechanical performances, microstructure, and durability were determined. The spongilite powder showed similar pozzolanic activity as natural zeolite or waste brick powder predicting an improvement in the mechanical properties and durability of prepared mortars. As the replacement level in lime mortars increased, the amount of mixing water needed for the same mortar consistence decreased, and the performance properties of the mortars improved. The increase in strengths of mortars was manifested mainly in the long term of 180 and 365 days. The incorporation of fine spongilite led to the formation of slightly denser, more water absorptive, however, more frost resistant and salt crystallization resistant structure in air lime mortars. The effective use of spongilite powder as a supplementary material in air lime mortars was assessed to enhance their performance in building practice or to prepare feebly hydraulic mortars used in the past in constructions nowadays considered built heritage.

The selection of building materials for any restoration project presupposes knowledge of their physico-mechanical properties, as compatible materials with the authentic ones need to be chosen at all times. In the case of composite building materials, such as lime-based mortars, the constituent raw materials, especially the aggregates which comprise the largest proportion of their volume, may affect the physico-mechanical performance of the end-product, both in the fresh and hardened states. It is therefore essential to identify the properties of the aggregates before these are incorporated in the mortar mixture. This paper reports on the effect of two different reef limestone crushed fine aggregates quarried in Cyprus on the physico-mechanical properties of repair lime-based mortars. The aggregates have been subjected to a series of standardized (i.e., soundness, Micro-Deval and water absorption) and non-standardized (powder X-Ray Diffraction) laboratory tests to identify their properties, before being used to produce lime-based mortars with fixed binder:aggregate ratio and workability. The results confirm the negative effect of poor-quality aggregates on the mechanical strength, the porosity and capillary absorption of the hardened end-products; this is corroborated through supplementary Mercury Intrusion Porosimetry (MIP), thermogravimetric (DTA/TG) analyses and Scanning Electron Microscopy.

In order to improve the properties of fresh and hardened lime mortars, inorganic substances of hydraulic or pozzolanic character have been added to the air lime already in the ancient times. The most commonly used natural pozzolans included tuffs, tuffites, diatomaceous earth, zeolitic rocks, trass or pumice. Although the use of natural pumice in lime mortars is known from history, professional work on the influence of finely ground pumice on the properties of air lime mortars is almost non-existent. Rather, the effects of coarse natural pumice used as aggregate in lime and cement mortars are described in the literature. For this reason, the paper aims to describe the effects of partial lime replacement with finely ground natural pumice on the mechanical, microstructural, and durability properties of air lime mortars. The ground pumice showed similar pozzolanic activity to trass or natural zeolite predicting an improvement in mechanical properties and durability. As the replacement level in air lime mortars increased, the amount of mixing water needed for the same mortar consistency decreased, and the performance properties of the mortars improved. The increase in strengths of mortars was manifested mainly for the 40% lime replacement. This mortar reached at 28 days of age the compressive strength comparable with hydraulic lime-based mortars. The incorporation of finely ground pumice led to the formation of slightly denser, less water absorptive, and more frost resistant and salt crystallization resistant structure in air lime mortars. Lime-pumice mortars showed improved properties in all important aspects from the point of view of the utility of these mortars in restoration and conservation interventions on historic buildings. Based on the achieved results, the 40% lime replacement was found to be optimal.

Historically, building stone was extracted and shaped by hand. To produce a flat surface using a mallet and chisel requires the time and energy of a skilled mason. As such, the highest level of workmanship was generally reserved only for the seen faces of stones. The joint surfaces were given less attention and would subsequently be “rougher”.In the modern era, diamond tipped gantry or wire saws are the standard equipment for stone processing. For the purposes of building conservation, the seen face of replacement stones are usually hand chiselled in keeping with the original design. However, it has become increasingly common for the joints of the new stones to be left as a clean diamond sawn surface.This paper examines if and how the difference in surface area between various stone surface finishes changes the characteristics of the lime mortar joint. The paper includes a surface area comparison of modern and historic stone surface finishes. This is followed by practical testing to ascertain how lime mortar joint/adhesive bond strength changes in relation to the amount of stone surface area available for adhesion.The results of the testing suggest a direct relationship between stone surface finish, joint surface area and lime mortar adhesion.

Research on injection grouting for the stabilisation of delaminated wall paintings and historic plasters mostly focuses on grouts based on aerial or hydraulic lime and on earthen-based grouting. Materials for the stabilisation of delaminated gypsum-based plasters have never been fully studied, even if gypsum has been used as a constituent material of wall paintings since ancient times. Grout mixtures developed during this research were specifically designed for the stabilisation of the 11th-century gypsum-based wall paintings in the Ateni Sioni church in Georgia. Due to the gypsum sensitivity to water, it was important to reduce the water content of the grout; this was achieved by partially substituting water with an alternative liquid, i.e. ethanol. The grout mixture design involved laboratory testing to assess the working properties and some performance characteristics of the grouts. In addition to the regular tests, grouts were injected into replicas simulating the challenging horizontal delamination present in the vaults of the church. The research proposes gypsum as the binder for a grout together with the use of a water-reduced dispersion medium, aiming to stabilise delaminated gypsum-based plasters.

Heritage air lime mortars are highly porous, flexible and allow the egress of moisture from the structure by the property of breathability. Commercial dry hydrated lime mortar is widely used to repair heritage structures. The binder is manufactured by adding water to the crushed quicklime; hydrated lime gets converted to calcium carbonate (CaCO3) by absorbing atmospheric carbon dioxide. CaCO3 exhibits different morphology such as calcite (most stable form), vaterite (least stable form) and aragonite, depending on the local conditions of temperature, pH, carbon dioxide concentration etc. Acicular aragonite can be present during the initial stages of carbonation. Amorphous Calcium Carbonate (ACC) could also exist initially as small spheres.The present study focuses on carbonating dry hydrated lime mortar in accelerated carbonation condition (3% CO2) to investigate the effect of CO2 concentration in the morphology of calcium carbonate formed. The study examines the extent of carbonation at various ages of the mortar specimens using the Phenolphthalein indicator test and X-Ray Diffraction (XRD). Morphology of the calcium carbonate crystals is examined using Scanning Electron Microscopy (SEM). The study is expected to provide insights into the relationship between CaCO3 polymorphism and carbonation condition in dry hydrated lime mortar mixes.

The rock-cut chapel of Niketas the Stylite (Cappadocia, Turkey) is decorated with 7–8th C CE painted gypsum plasters on a tuff support. A 2015 survey found that detached areas of plaster required stabilization through injection grouting. This paper presents the rationale behind the preliminary development of calcium sulfate hemihydrate (HH, CaSO4·0.5H20)-based injection grouts for this purpose and their testing in the field. Research into gypsum-based conservation materials is limited compared to lime, and there are very few examples of the development of proprietary gypsum grouts for the stabilization of wall paintings on gypsum plaster. This study therefore reviews the existing literature, and explains the rationale behind the selection of materials for the conservation of the paintings, including a discussion of the potential risks and benefits associated with the use of lime and gypsum binders. Field testing focused on the development of HH-based grouts formulated with a range of aggregates and fluidizers. The grout mixes were tested against clearly-defined working properties and some of the performance characteristics for the intervention. Existing field-testing protocols were adapted as necessary to the working conditions, context and materials of the site and paintings.

Development of new solutions for masonry mortars is heavily reliant on laboratory-based experimental procedures. This study provides insights into the properties of masonry mortars, prepared by four distinct compaction methods, based on existing standards: tamping, tapping, jolting and vibrating. The particular mortar mix under study has been designed in volumetric proportions of 1:1:6 with air lime, cement and sand, respectively. Evaluation of differences among compaction methods is based on bulk density, mechanical strength, porosity and water absorption measurements at 7 and 28 days. Density and strength testing results indicate statistically significant differences, where mechanically compacted mortars are denser and stronger than their manually compacted counterparts. Similar development is observed through assessment of mortar porosity. The variation is noticeable in gel and capillary pore range as shown by mercury intrusion, while open porosity evaluated by vacuum immersion also indicates some distinction between manual and mechanical compaction, with the latter producing less porous mortars. On the other hand, capillary water absorption results reveal higher coefficients for jolted and vibrated samples, hinting at different pore interconnectivity in mechanically and manually compacted mortar specimens.

The Paimogo Fort, listed as a public interest property in 1957, is one of the several Portuguese military fortifications built near the ocean, in the 17th century. Within the scope of the restoration project developed by the Municipality of Lourinhã and its partners, for the revitalization and safeguarding of the Paimogo’s Fort, an extensive characterization of the original mortars was made and new repair mortars are being developed by National Laboratory for Civil Engineering.In the present work the development of the durable and compatible repair mortars for this case study is described. Some compositions based on the original mortars’ composition and characteristics are briefly described and their main physical and mechanical characteristics are analysed and compared in successive ages. Applications of the same mortars on porous composite substrates were subjected to real environmental conditions in the Fort external area to check their performance and durability.The experimental results showed the importance of the in situ applications, since distinct behaviour was found. Moreover, it reveals that all the studied mortars absorb higher volume of water and have lower strength and higher deformability, when compared to the original ones. Thus, the choice of the formulations for application as a substitution render of the Fort walls is still in process of evaluation. Their performance and durability are being studied at longer ages and the formulations will be fine-tuned for further evaluation.

Various tests have been developed to evaluate the reactivity of some pozzolans to study the feasibility of using an accessible deposit, without the need of importing or transporting materials. Pozzolanicity tests mostly require sophisticated and expensive laboratories. For some conservation projects, this type of analysis is out of reach due to the complexity of analysis, their elevated costs, and the time it takes to carry them out. A. D. Cowper in 1927 describes a simple and on field test to determine if a material has pozzolanic activity, but it is not deeply explained why samples of materials with possible hydraulic action can be tested, after seven days in a qualitative indication of hydraulicity. In this research, pozzolanicity reaction and flocculation process are reviewed, the Cowper Test is implemented, and new simple procedures are added to corroborate the Cowper Test efficiency. The increase of volume due to flocculation, sedimentation velocity, observation in microscope, changes in pH and changes in refractive index are applied and discussed. This is a contribution to transit from a qualitative test into a semiquantitative, it is expected to be the fundament that can lead into a future on field quantitative method for determining pozzolanicity.

Although, the salt crystallization is one of the most common causes of the deterioration of lime-based mortars, testing of their resistance to the soluble salt action has not yet been standardized. The problems following the development of the globally accepted testing method are, among others: defining the type of mortar samples, ways of samples’ contamination, the type and the concentration of the salt solutions used, environmental conditions during testing, determination of the damage development and the durability assessment. Another task of the testing method is to explain and connect the processes developing in the materials when they are applied in laboratory and real conditions. In this paper, soluble salt resistance testing of lime mortars on the composite samples is presented. The main focus of the paper is on the determination of the salt distribution in this type of samples after the five wetting and drying cycles. Samples consisted of two lime rendering layers (inner – 1/3 and outer – 1/1), both prepared according to the experiences found in the literature for these types of lime mortars when applied on historical structures, placed on the natural stone bases. They were cured in laboratory conditions for 90 days, before drying and exposing to soluble salts action. Two types of 10% salt solutions were used for the test: sodium-chloride and sodium-sulfate. Salt contamination was performed by capillary action only in the first cycle, while in the other cycles samples were wetted by deionized water. After the finalization of the cycles, the detached pieces of mortar and efflorescence were removed from the samples. One of the samples from both groups were then cut in two halves, from which one was used for X-Ray Fluorescence (XRF) and another for Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM – EDX) characterization. For the XRF analysis samples were divided into four layers, and then crushed and sieved through 0.5 mm sieve before testing. For the SEM-EDX analysis the polished thick cross sections were prepared. The paper presents the results of these two analyses, and discusses the advantages and disadvantages of their application for this purpose. Mineralogical analysis of the samples was performed using XRD analysis. It was shown that XRF analysis provides more precise quantification of the elements within one sample, while SEM-EDX analysis gives possibilities for testing of layers with smaller depth within one cross – section.

A thin grout was designed and tested for the stabilisation of the 16th c. Perez d’Aleccio’s wall painting cycle of the Great Siege, in the Grandmaster’s Palace in Valletta, Malta. The painting, on a single layer of lime-based plaster applied on Globigerina Limestone, presented delaminated pockets up to 5 mm thick, with narrow access points ≤1.5 mm wide (cracks) to inject the grout. For this reason, the grout could just be injected through very fine needles, a 18G (0.84 mm inner diameter) and/or 19G needle (0.69 mm inner diameter). Considering the porous original plaster, to avoid a reduction in porosity of the grout observed in previous studies, the site-specific grout was designed without the use of additives such as superplasticisers, and included just binder (slaked lime putty), aggregates, water. Different aggregates were selected and tested in different proportion, the variables for their selection being: particle shape, particle size and water absorption. Testing of the grouts included: injectability, flow on plastered tile, bleeding, shrinkage and adhesion in Globigerina Limestone cups, cohesion. A very thin grout, passing through a needle 0.69 mm wide, was obtained, without the use of superplasticisers, relying only on the role of aggregates and their particle size and morphology.

Microencapsulated Phase Change Materials (PCMs) were included in air lime rendering mortars in order to improve the thermal comfort of the inhabitants and the energy efficiency of buildings of the Architectural Heritage under the premises of minimum intervention and maximum compatibility. Three different PCMs were tested and directly added during the mixing process to fresh air lime mortars in three different percentages: 5, 10 and 20 wt. %. Some chemical additives were also incorporated to improve the final performance of the renders: a starch derivative as an adhesion booster; metakaolin as pozzolanic addition to shorten the setting time and to increase the final strength; and a polycarboxylated ether as a superplasticizer to adjust the fluidity of the fresh renders avoiding an excess of mixing water. The specific heat Cp, the enthalpy ΔH ascribed to the phase change and the melting temperature of the PCMs were determined by Differential Scanning Calorimetry (DSC). The capacity of the renders to store/release heat was demonstrated at a laboratory scale. The favourable results proved the effect of these PCMs with respect to the thermal performance of these rendering mortars, offering a promising way of enhancement of the thermal efficiency of building materials of the Cultural Heritage.

Different batches of repair lime rendering mortars were designed by mixing microencapsulated Phase Change Materials (PCMs) and other additives. The final aim of these renders is to improve the thermal efficiency of the envelope of the Built Heritage, while allowing the practitioners to apply a render with positive final performance. The combinations of the PCMs in different weight percentages, a superplasticizer (to increase the fluidity of the render keeping constant the mixing water), an adhesion improver and a pozzolanic additive were studied. The adhesion of these renders onto bricks and limestone specimens and the shrinkage and cracking of the mortars were studied in detail. X-ray diffraction technique was used to study the composition and evolution of the carbonation process. Compressive strength measurements were studied in hardened specimens. In addition, the porous structure of the rendering mortars was studied by mercury intrusion porosimetry to assess the effect of the PCMs’ addition. Results have shown that these thermally enhanced mortars are feasible materials for real-life application in the context of architectural heritage restoration and conservation.

Lime-based mortars are preferred in repairing interventions of Historic Masonries (HM), which are the bearing elements of old structures, since they are considered compatible with the existing mortars. In historic castles, towers and particularly in cases of thick mortar joints reconstruction, long term deformations are of great interest for the structural stability of the repaired monuments. The exposure of lime-based mortars to drying and sustained loading influences both phenomena of shrinkage and creep. In this experimental work, the behaviour of different composition mortars (based on hydrated lime, lime-pozzolan, hydraulic lime and lime+pozzolan+cement) have been studied under sustained load by using spring-loaded creep frames.The same types of mortars were also used for the masonry specimens with traditional roman type bricks in successive layers. All specimens, mortar prisms (4×4×16) cm and masonry specimens were placed in a moisture-controlled room of RH 55–65% and 20 °C temperature. Bricks and mortars’ compressive strength have been separately estimated by crushing proper samples. Deformations were recorded for more than 6 months because of drying and sustained loading. It seems that the strain measured is higher than in the case of cement-based mortars/ concretes. Furthermore, for thick joints the composition of mortar and its quality, expressed as compressive strength play a crucial role in the total deformation measured apart from the sustained load value. In addition, the rate of creep evolution and the order of creep magnitude are indicated.

Commercially non-structural injection grouts often contain cellulose ether as an additive, mainly to modify the viscosity and stability of the grout. Nevertheless, in our previous field studies we observed mould growth after injection of commercial grout that contained methyl cellulose (MC) as an additive. Therefore, our objective was to determine the effect of MC on mould development after grouting of painted plaster layers. For this purpose, a painted panel sandwich model, simulating delaminated plaster layers, was inoculated with fungal strains isolated from various cultural heritage sites. After incubation (27 days), mould growth was assessed using Calcofluor white fluorescent staining. Our preliminary results show that during the incubation the moisture content on the surface of the dry part of the model increased steadily due to the high humidity in the chamber and the absorption capabilities of the porous plaster. Moreover, grouting increased the moisture content on the surface of the paint layer by ~10%. As a result, fungal stains EXF-15333 and EXF-15047 grew exclusively on the dry injected part of the surface (growth of 30%) and no growth was observed on the dry non-injected part. Alarmingly, when the mortar was removed, it was revealed that the injected grout in the air pockets had not cured after 27 days.