Lime-based Mortars Research Articles

Effects of Sugarcane Bagasse Fiber Additives on the Mechanical Properties of Lime-Based Composites and their Compatibility with Traditional Lime-Based Mortars

This study explored the incorporation of sugarcane bagasse fibers into lime mortars to potentially enhance the mechanical properties and durability of materials used in heritage structures made of unreinforced masonry. Assessment of the mixes and their compatibility with the traditional lime mortar mix used in conservation projects in the Philippines was also performed. Five (5) mortar specimen types containing different fiber content were prepared, each with twelve (12) samples. Flexural strength, compressive strength, ductility, and modulus of elasticity comprise the mechanical properties investigated while visual properties, chemical and mineralogical composition, pore space, mechanical properties, and hydrophilic behavior comprise the criteria for computing incompatibility degrees (IDs). Being the mix traditionally used in local conservation works, Mortar L0 (plain mortar) served as the control. Results showed that Mortars L4.6 (4.6% fiber content), L7.6 (7.6% fiber content), and L10.7 (10.7% fiber content) generally had lower mechanical properties compared to Mortar L0, except for the 14% increase observed in the compressive strength of Mortar L4.6. Mortar L1.5 (1.5% fiber content) had the best results having significant improvement in overall mechanical strength. It exhibited 6.8% increase in flexural strength, 38% increase in compressive strength, and 69.4% increase in modulus of elasticity values. Mortars L1.5, L4.6, L7.6, and L10.7 were computed to have IDs equal to 3.6, 1.1, 1.8, and 3.3, respectively. These indicate low to medium low incompatibility with Mortar L0. These findings highlight the viability of sugarcane bagasse fibers as reinforcement for lime mortars while maintaining sufficient compatibility with traditional lime mixes.

A Research on Developing Zeolite Based Lime Mortars

Zeolites are aluminosilicate materials that possess a crystalline structure characterized by an interlinked three-dimensional framework of AlO4 and SiO4 tetrahedra. This framework contains open cavities in the form of channels and cages, leading to the designation of zeolites as molecular sieves. The characteristics of molecular sieves enable zeolites to have high adsorption capacity, ion exchange capability, and catalytic properties, which also contribute to improving indoor environmental quality. Zeolites also exhibit pozzolanic reactivity due to their high silica content. These chemical and physical properties of zeolites offer the potential to produce a lime-based mortar with improved mechanical performance, which can also contribute to the physical conditions of the environment with its hygroscopic behavior. For this purpose, under the scope of the research, the pozzolanic reactivity of zeolite obtained from the Manisa Gördes region of Türkiye has been evaluated first. After establishing the pozzolanic property of zeolite, mortar alternatives with different pozzolan/binder ratios, curing conditions, and aggregate sizes are investigated through a combination of physical and mechanical testing methods. Clinoptilolite-type natural zeolite in the form of powder and aggregates, which vary between 0-7 mm (0-2 mm, 2-4 mm, 4-7 mm) particle size, and class CL 90 – S type slaked lime were used to produce zeolite based lime mortars. The different particle sizes of zeolite aggregates were added to increase the moisture adsorption capacity of the mortar.

Diagonal Compression Tests on Unfired and Fired Masonry Wallettes Retrofitted with Textile-Reinforced Alkali-Activated Mortar

This paper discusses the integration of an alkali-activated mortar (AAM), based on industrial waste, into a novel composite material fit for structural upgrading purposes and rendered with high temperature endurance and a low CO2 footprint. The AAM combined with carbon fiber textiles form a new generation of sustainable inorganic matrix composites—that of textile-reinforced alkali-activated mortars (TRAAM). A test program was designed to assess the effectiveness of carbon TRAAM overlays in increasing the shear capacity of masonry wall specimens comprising solid clay bricks bonded with lime-based mortar and furnished with TRAAM jackets on both sides. The initial and the residual capacity of the reinforced walls were evaluated, the latter by performing diagonal compression tests after exposure to 300 °C and 550 °C. It was shown that TRAAM jacketing can increase the shear capacity of unfired masonry walls by 260% and 335% when a single or a double layer of textile is used, respectively. Rapid heating to temperatures up to 550 °C, one-hour-long steady-state heating, and natural cooling bore no visible thermal cracks on the specimens and had little effect on their residual capacity. Based on these results, the prospect of using TRAAM for retrofitting applications for fire-resilient structures seems very auspicious.

The diagonal shear behavior of masonry walls fabricated with historical lime-based mortar and retrofitted with near surface mounted method

The historical monuments in different regions of the world were constructed using local materials. Sarooj was a lime-based mortar utilized extensively in the construction of Unreinforced Masonry (URM) buildings in some Middle Eastern countries in the past centuries. However, few studies have been conducted on the mechanical properties of masonry fabricated with Sarooj and strengthening of the elements in which this type of mortar was used. In the present study, the in-plane shear behavior of URM wallettes fabricated with Sarooj mortar and retrofitted with Near Surface Mounted (NSM) Glass Fiber Reinforced Polymer (GFRP) bars is investigated through an experimental and numerical study. In this regard, first, diagonal shear tests are conducted on square wallettes. The test specimens include bare and retrofitted wallettes. The type of paste used for filling the grooves in the NSM method and the retrofitted face of the wallettes are the main variables whose effects are investigated in the experimental program. In addition to the NSM method, the in-plane behavior of walls retrofitted with a novel technique named Epoxy Filled Joint (EFJ) is investigated in the experimental phase of the present study. Then, through a numerical study, the wallettes retrofitted with the NSM method are simulated in Finite Element (FE) software Abaqus following a macro-modeling approach. The results of the experimental study confirmed that the strengthening of the URM wallettes with the NSM method not only enhanced their ultimate in-plane shear strength, but also improved the ultimate drift capacity of the wallettes. Furthermore, the shear stress-drift curves obtained from the FE model were in good agreement with those obtained from the tests. In addition, the test results showed that the EFJ method significantly increased the in-plane shear strength of the wallettes.

Production of environmentally-friendly, high-strength repair mortar for the restoration of historical buildings

In this study, repair mortars with artificial and natural pozzolan additives were produced for the restoration of historical buildings. Class C fly ash, an artificial pozzolan and zeolite the natural pozzolan, were substituted into these lime-based mortars. Two different aggregate types were used in the preparation of the mortars: natural river sand and crushed brick. A total of 18 batches of mortars were produced, two of which were reference batches. In the first group of batches, fly ash, which is the major pozzolan, was tested in both aggregate groups in 20%, 40%, and 60% ratios of lime substitution. In the second group of batches, fly ash and zeolite were used in different proportions as lime substitution. In the reference series, air lime was used alone. At the end of the 28, 56, and 90 days curing period, mechanical, physical properties, and phase composition of the mortars were determined. When the pozzolan-added mortars were compared with the reference mortars, it was observed that pozzolans provided significant improvements in the physical and mechanical properties of the repair mortars. While significant improvements were observed in the physical properties of the mortars where fly ash was used as the only pozzolan, mechanical properties were better in the mortars with zeolite.

Durability tests on lime-based mortars from the historic built heritage of Catania (Eastern Sicily, Italy): An experimental study

Mortars, like any other natural and artificial stone materials, are subject to atmospheric weathering agents which affect their durability according to the intrinsic characteristics of the material, such as mineralogical composition, texture and pore structure.This paper aims to investigate the physical-chemical durability of lime-based mortars made with two different volcanic aggregates, locally known as azolo and ghiara, peculiar of the historic built heritage of Catania (Eastern Sicily, Italy). An experimental approach has been used, based on the reproduction in laboratory of historic mortars by using ancient recipes. The experimental samples have been characterized from a physical point of view and then subject to accelerated aging tests. Specifically, the samples have undergone: i) mineralogical investigations through X-ray diffraction (XRD); ii) thin section analysis by polarized optical microscopy; iii) pore structure analysis through mercury intrusion porosimetry (MIP); iii) water absorption by capillarity; iii) water vapor permeability test; iv) accelerated aging test by salt crystallization; v) decay by sulfur dioxide.Results obtained highlight that the higher microporosity which characterizes the ghiara mortars is certainly responsible for their greater water absorption by capillarity as well as for their lower resistance to salt crystallization and exposure to sulfur dioxide, with respect to azolo-based ones.

Lightweight pumice mortars for repair of historic buildings –Assessment of physical parameters, engineering properties and durability

The subject of the presented research was an experimental analysis of physical, engineering and durability parameters of lightweight mortars intended for the repair of historical buildings. Compatibility criteria, the requirements of technical standards and guidelines, and last but not least, previously published research results dealing with the development of mortars for repair delicate historic structures were taken into account in the design of mortar composition. Crushed pumice of a similar grain size was used to lighten the reference lime-based mortar and natural hydraulic lime mortar with quartz filler. Replacement of quartz sand with pumice was 25, 50, 75 and 100% by volume. The use of pumice allowed the fundamental physical, mechanical, hygric, thermal and durability parameters of the lightweight mortars to be such that they met the standard requirements for repair mortars and the heritage conservation requirements for compatibility with the original materials of historic masonry. The main finding was the fact that by replacing sand with pumice, a significant increase in the porosity of the mortars was achieved, while maintaining sufficient mechanical strength due to the pozzolanic reaction of the pumice. Mortars based on natural hydraulic lime have become more resistant to frost and salt crystallization. The advantage of the developed mortars was their low thermal conductivity and high water vapor permeability, which made them suitable for use on damp masonry, which is a substantial scientific contribution of the manuscript.

Experimental Investigation on Comprehensive Performance of Natural Hydraulic Lime-Based Mortars: Effect of Waterproof Admixtures Addition

ABSTRACT In this study, the bulk modification method via incorporating two different types of waterproof admixtures was adopted to make natural hydraulic lime-based mortars more durable. The influence of two admixtures and their dosages on the hydration, physical, mechanical, and aggressive environment resistance properties were evaluated. The correlations between pore and water absorption characteristics, between hydration, pore characteristics, and mechanical strength were interpreted. Results showed that two waterproof admixtures changed the microscopic reaction between different components as well as internal structure of NHL-based mortar. Introduction of silane impregnant improved the workability of natural hydraulic lime-based mortars, and the appropriate dosage of silane impregnant facilitated hydration and improved mechanical strength at 28 and 90 days. Silane impregnant modified mortars were no more hydrophilic, acid resistance was improved while water absorption characteristics were not obviously improved even resulting in degraded freeze-thaw cycle resistance. Introduction of silicon-acrylic latex deteriorated the workability and retarded hydration of natural hydraulic lime-based mortars, regardless of dosage, leading to the degradation of mechanical strength. However, water absorption characteristics and freeze-thaw cycle and acid resistance can get a noticeable improvement when appropriate dosage was adopted.

Proposal of New Natural Hydraulic Lime-Based Mortars for the Conservation of Historical Buildings

NHL mortars are known to be compatible materials for the conservation of architectural heritage. To improve their properties with regard to salt resistance and lower their carbon footprint, NHL-based mortars with salt inhibitor agents were studied and different formulations were produced: NHL-based mortars (MSs), composed of natural hydraulic lime; and sand and cocciopesto mortars (MSCs), in which NHL, sand and brick powder were admixed with two different products, diethylenetriaminapenta and chitosan, in different concentrations. The mortar performance was tested against freeze–thaw and salt crystallization through immersion–drying cycles in a 14% sodium sulfate solution. The results highlighted that the addition of cocciopesto was effective in increasing the salt resistance, but increased the water intake during the freeze–thaw tests. The use of DTPMP produced less thixotropic mortars and decreased the water uptake, but worsened the salt resistance of hardened mortars. Chitosan allowed a good workability of fresh mortar; its water uptake was similar to the reference mortar and slightly increased the salt resistance. In the cocciopesto samples, both additives reduced the weight variation during freeze–thaw tests; meanwhile, for the lime samples, the additives increased the weight variation during the final cycles.

Utilization of waste animal blood as an additive in hydraulic lime-based mortars

Animal blood, which makes up approximately 4% of an animal's weight, is the primary by-product obtained during the slaughter process. However, most animal blood produced in developed countries is discarded in sewers and landfills. Despite some existing research on the use of waste blood in various materials, there still needs to be further improvement in preparation methods, applications, and the performance of building materials. To address this issue, this study investigates the potential use of waste animal blood as a chemical additive in hydraulic lime-based mortars. The aim is to examine its impact on the physical, rheological, mechanical, microstructural, and durability characteristics of these mortars. The results indicate that adding waste animal blood effectively reduces capillary water absorption and significantly improves the freeze–thaw resistance of lime-based mortars. Therefore, this study suggests that waste animal blood can be a promising and sustainable alternative additive for producing durable construction materials.

On the use of non-destructive testing for the measurement of self-healing in lime-based mortars

The study of self-healing construction materials has increased in popularity over the last couple of decades. Nevertheless, most research has predominantly focused on cement-based materials and work on other type of binders such as lime-based mortars remains rather limited. Despite the multiple testing methods available to assess the efficacy of self-healing, these techniques are not always suitable for materials of different mechanical strengths and behavior. In order to further expand the knowledge on self-healing beyond the high-strength cement-based materials, self-healing has been studied on low-strength binders. Here it is shown how the use of non-destructive testing with ultrasonic pulse velocity (UPV) can help determine the self-healing capacity of low-strength mortars. A hydrated-lime:metakaolin mortar mix and cement mix were cast and damaged after 7 days of curing. The samples were damaged under compression using 70 % of the average compressive strength. Before and after damaging, the samples were tested by UPV and superficial cracks were studied by microscopy. The samples were then placed under wet-dry cycles of 1 h wet/23 h dry or submersion for 28 days and tested again. As healing proceeded, an increase in the UPV was observed. Microscopy measurements confirmed visually the self-healing of cracks in all samples. The mechanical strength of both formulations was similar after healing when compared to a non-damaged and non-healed sample. These results show the necessity for techniques that are tailored to the mechanical nature of the different studied materials and opens up the possibility of further investigating self-healing in a wider variety of construction materials.

Behavior of unreinforced multi-leaf stone masonry walls under axial compression: Experimental and numerical investigation

This paper presents an experimental and numerical investigation on the behavior and failure mechanisms of unreinforced multi-leaf masonry walls. The main objective of this study is to explore the propagation of cracking, ultimate load, and deformation characteristics of different typologies of three-leaf walls commonly found in historic masonry. Axial compression tests on scaled three-leaf wallettes built of limestone units and lime-based mortar, as well as experiments on constituent materials for each leaf, were carried out. The main results obtained from the experimental tests are the mechanical characteristics, stress–strain curves, stress distributions in multi-leaf masonry walls. The research findings elucidate a strong correlation between the bearing capacity of multi-leaf walls and the thickness ratio of the inner-core layer to the external layers. This relationship underscores the critical significance of the inner-core layer in efficiently carrying the applied vertical loads. Furthermore, the extent to which the inner-core layer actively contributes to load-bearing is contingent upon the interconnectivity among the three layers. Walls with keyed collar joints have a higher strength and stiffness than the walls without transverse tying, with the strength being comparatively higher by about 9–13 %. This clarifies the contribution of the inner core layer and that of the two outer layers in resisting vertical loads and enhancing the overall composite behavior of the wall. Finally, these results allow for validating non-linear numerical procedures based on two-dimensional plane strain modelling along wall thickness and a simplified micro-modelling approach, which prove to be adequate tools for detailed modelling of masonry components of similar nature.

How to improve the cradle-to-gate environmental and economic sustainability in lime-based construction materials? Answers from a real-life case-study

A real-case study is presented aiming at contributing to the understanding of environmental and economic sustainability of lime-based mortars, renders and plasters manufacturing in Europe. A Life Cycle Inventory is presented and used for scenario analysis. The Life Cycle Assessment shows that the binders’ production dominates the Climate Change, Resources and Ecosystem quality categories while additives are critical in Human Health. The CO2 emissions can have a direct impact on the total costs (up to 40%) considering the 2022 carbon pricing. A holistic analysis and suggestions (mix composition and critical processes) to increase the sustainability in the sector is provided.

RILEM TC 277-LHS report: additives and admixtures for modern lime-based mortars

The scope of this collective paper produced in the frame of RILEM TC 277-LHS is to provide sound knowledge on the use of additives/admixtures in lime-based mortars, based on literature and practice. The most widely known additives/admixtures are systematically presented. Their main effects and testing of their performance have been properly tabulated. It is well known that a plethora of additives/admixtures are produced every year by chemical industries. However, when using them in lime-based mortars, compatibility and durability aspects are of primary importance. The introduction of additives/admixtures in lime mortars was imposed by the need to improve important properties of these composites in the fresh and hardened state, namely, workability, durability, early-age and long-term strength and to reduce defects, such as shrinkage and long setting time. In this review paper, the terminology proposed by EN 16572 is followed, designating additive as a constituent added in small quantity to the binder, and admixture as a substance in quantities at least 1% w/w added to the mix. The additives/admixtures are classified according to their action and their validation with specific testing methodologies highlights the dosage sensitivity and the need to develop further standardization. The combination of different additives proposed in several studies resulted as the most promising strategy to enhance the performance of lime mortars. However, recently developed additives and admixtures need to be further evaluated with reference to their compatibility with other mortar constituents, and their effects on the overall mortar and render durability need to be studied. Finally, adopting similar terminology for additives/admixtures in lime and cement-based mortars will facilitate better comparison and assessment issues.

Lime-based mortars with added silica fume and bioproducts for restoration and preservation of heritage buildings

Restoration of heritage buildings requires an appropriate choice of materials, as inappropriate materials can lead to degradation rather than preservation. Hydrated lime and sand mortars are the most suitable for masonry cladding. However, they have low durability regarding current requirements. This work investigates the use of silica fume and/or biopolymers (egg albumen and additive derived from the reuse of milk unfit for human consumption (complexes of whey protein with κ-casein) in producing these mortars. Some mortars were characterized by mechanical properties (compressive and diametric strength, absorption rate) and chemical properties (SEM, Infrared spectrum). The research revealed that silica fume addition allows an increase of more than 50% in the mechanical strength of the mortars when associated with animal protein. The value may be higher than 60%, especially for biopolymers (complexes of whey protein with κ-casein). Finally, the proteins in the mortar mixture provide intense air entry that results in the formation of more pores. This increase in voids allows more CO2 to enter, directly contributing to a faster carbonation process and performance mortar.

The effect of animal and synthetic fibers on the physico-mechanical durability and microstructure properties of natural hydraulic lime-based mortars

This paper aims to study the effect of adding horsehair (HH), polypropylene (PF), carbon (CF), basalt (BF) and glass fibers (GF) on the physico-mechanical durability and microstructure properties of natural hydraulic lime-based mortars (NHL). The studied fibers were added to the mixture at 0.3 %, 0.6 %, and 1.2 % by weight of NHL and compared with plain NHL mortar. The workability (flow diameter test), physical (dry bulk density and water absorption), compressive strength (fc) and flexural strength (ff) (at 7 and 28 days) were tested. The durability was tested by water penetration depth (Wd), NaCl and Na2SO4 salt crystallization and exposure to the wetting-drying (W-D) cycles in Na2SO4, as proved by XRD. Scanning electron microscopy (SEM) of samples after 28 days of curing. From the results, it can be concluded that HH3 (0.3 % fiber) has the highest dry density (1794 kg/m3), fc and ff at 28-days (13.3 and 4.2 MPa), and resistance of all salt crystallization tested, smallest water absorption percentage (16.2 %), and water penetration depth (38.23 mm) of all mortars. On the other hand, it can be noted that adding synthetic types of fibers reduced the dry density and increased water absorption. The XRD explained that immersion or exposure to (W-D) cycles of Na2SO4 has a worse effect on hydration than NaCl exposure. The SEM shows that fiber-filled lime mortar's mechanical properties and durability are improved through the conductive network, especially HH, which had a large diameter with a rough surface and indicated a sufficient level of adhesion with the matrix.

Effect of ceramic waste powder as a binder replacement on the properties of cement- and lime-based mortars

Ordinary Portland cement (OPC) is responsible for 8% of worldwide carbon emissions and the construction industry is in need of alternatives to minimise its impact. Waste products from foundries and furnaces are prime candidates as they can be high in reactive properties. This paper reports on the results of an experimental investigation into the effect of ceramic waste powder (CWP) as a binder substitute in cement and lime-based masonry mortars. As part of a comprehensive experimental investigation, standard cement and lime specimens were made with replacement rates of 0–60% and 0–80%, respectively, and moist cured for up to 90 days. The examined properties include compressive strength, tensile strength, dry bulk density and permeable voids, drying shrinkage, and pH. Based on the obtained results, the compressive and tensile strengths of cement mortars containing CWP not only experienced no significant adverse effect up to 50% replacement, but also increased at the substitution percentages of 10–20%. For the hydrated lime mortars, the compressive and tensile strengths were continuously enhanced up to 70% replacement of lime with CWP. These results were supported by the outcomes of the scanning electron microscopy (SEM) images and X-ray diffraction (XRD) analyses. These findings can introduce a useful application of CWP as a sustainable binder replacement in construction leading to reducing the carbon footprint of construction materials and the adverse environmental impact of CWP disposal in landfills.

Carbonation of air lime mortars under natural and accelerated conditions – A systematic review

Lime was a prominent building material in ancient times that was replaced by cement by virtue of its fast application properties. The use of lime as a construction and repair material is gaining significance recently as the conservation of heritage structures has become a concern. Moreover, the CO2 associated with the production of cement is proliferating. The use of cement mortars in repairing heritage structures did not prove to be a good choice as the composition, characteristic properties and strength were very different to that of lime binders and therefore reduced the breathability of the existing structures. Lime mortars generally react with the CO2 present in the atmosphere to gain strength and this property of lime can be employed to use it as a CO2 sink. However, the time associated with the reaction is quite high and the present systematic review focuses on the methods by which the CO2 absorption process can be accelerated. The influence of various organic and inorganic additives in accelerating the reaction in natural and high CO2 environments is critically compared. The influence of carbon curing the lime-based mortars on mechanical and microstructural properties is studied. The current review critically compares the behaviour of lime mortars in the mentioned conditions and gives an insight into the amount of future work to be done to promote lime-based binders commercially.

Lime-based mortar reinforced with randomly oriented polyvinyl-alcohol (PVA) fibers for strengthening historical masonry structures

The seismic vulnerability of unreinforced masonries underlines the importance of developing new methods and materials for the retrofitting of historical structures. Nowadays, two are the most widely diffused strengthening systems for masonry structures, i.e. fiber reinforced polymers (FRP) and fabric reinforced cementitious matrix (FRCM) composites. Despite some degree of effectiveness, FRPs show poor chemical compatibility with masonry supports, that makes them unsuitable for intervention on historical heritage structures. FRCMs frequently consists of a cement-based mortar and, because of this, the cementitious nature of the inorganic matrix can not ensure the chemical compatibility with the historical masonry substrate; also, being FRCMs composites made out of fiber fabrics embedded in an inorganic matrix, the mono- or bi-directionality characterizing the fiber fabric makes this type of reinforcement ineffective out of the fiber axial direction. This paper aims to overcome the listed drawbacks presenting a systematic study on a newly developed lime-based mortar, reinforced with randomly oriented polyvinyl alcohol (PVA) fibers: the lime-based nature of the mortar meets the requirement of chemical compatibility with the historical substrate, that is fundamental for the restoration of heritage buildings, and the random orientation of the PVA fibers makes them globally effective, being the stress state induced by seismic action directionally unknown. Specimens measuring 160 mm × 40 mm x 40 mm characterized by six different fiber contents and two different fiber lengths, namely 6 mm and 12 mm, in addition with plain mortar samples, are tested in three-point-bending configuration to compute both flexural strength and fracture energy. Then, the two broken pieces resulting from the flexural tests, each one measuring 80 mm × 40 mm x 40 mm, are tested in splitting configuration and in compression, and the resulting tensile strength and compressive strength are computed. An analytical formulation is finally proposed by fitting the experimental data with linear, parabolic and exponential regression models. The results related to averaged values of mechanical properties show that, for both short and long fiber lengths, the flexural strength and the fracture energy linearly increase with the fiber content and that the tensile and the compressive strengths parabolically increase with the fiber content. Overall, the newly proposed mortar stands as a valid system for the strengthening of masonry structures, being especially suitable for intervention on cultural heritage buildings.

Inventing Tradition in Bhaktapur, Nepal: The Trajectories of Lime in Heritage Reconstruction

Abstract: In this paper, we trace the evolution of discourse, policy, and practice that have legitimized lime as a "traditional" building material in ongoing heritage reconstruction in Bhaktapur, Nepal, following the 2015 Gorkha Earthquake. While historically much of Bhaktapur's architectural fabric has used brick and timber as structural systems along with mud-(or clay-)based mortars and finishes, lime-based mortars and plasters have become ubiquitous as a material for heritage reconstruction. The benefits of lime over mud in terms of material strength are cited as one reason. Diminishing sources for mud are attributed as another reason, even as lime is imported extensively from neighboring countries such as India. Local contractors, officials, and laborers describe lime as a traditional building material, even though it was introduced as mortar relatively recently by UNESCO consultants working in the Kathmandu Valley in the 1970s and 1980s. In this paper we examine the materialities of lime and the narratives around its strength and seismic performance that contribute to its popularity. We analyze the ways in which lime as a material for heritage reconstruction gets simultaneously classified as traditional and modern, local and global, through a brief historiography of its use in Kathmandu Valley and by engaging with specific case studies in the Bhaktapur Durbar Square, which is a UNESCO World Heritage Site.