The history of the use of lime in the construction industry dates back thousands of years, spanning cultures and communities worldwide. In fact, around 4000 B.C., the ancient Egyptians used quicklime mixed with water as a building material for their pyramids. Although lime has multiple applications in the food and agricultural industries, as well as in chemical, mining, and steel industries, in architecture it is one of the main construction materials due to its versatility, adhesion, waterproofing, workability, performance, setting, and durability, which allow for the creation of masonry mortars, interior or exterior plasters, among other functions.
Although there are earlier civilizations that used lime mortars in the development of large structures, it is considered that the Romans were the first to use them in construction. More than 3000 years ago, the Cretan civilization in the Mediterranean used lime as a masonry mortar, and lime mortars were also used in the Great Wall of China. For example, the Pont du Gard aqueduct in Nîmes, in southern France, was built in 18 B.C. as a waterproofing case where a mortar based on hydraulic lime was used.
By the 18th century, Smeaton's work led to the understanding of the properties of hydraulic lime, which later resulted in the technology and patent of Portland cement. From the 19th century to the present, the advent of Portland cement (OPC) led to a significant decrease in the use of lime in construction due to its rapid initial hardening and greater early-age strength. However, appropriate use of lime in construction can involve, among other factors, production at lower temperatures than OPC and less energy during its calcination, resulting in lower greenhouse gas emissions and minimal shrinkage, preventing cracking.
Being an inorganic white powder material, lime is obtained from the calcination of limestone, a mineral composed of calcium carbonate. Once extracted from a quarry, the limestone is crushed, reducing its size to a maximum of 80 to 200 mm, and classified according to its granulometry. It is then calcined at high temperatures (between 900 and 1200°C), causing the release of carbon dioxide and leaving calcium oxide as a residue, known as quicklime. Finally, the quicklime is transferred to storage silos where it is distributed in bags or bulk. By incorporating water, quicklime is transformed into hydrated or slaked lime through an exothermic reaction that releases steam. In a separation and grinding circuit, normal hydrated lime is obtained, while passing dolomitic quicklime through a hydrator and grinding produces pressure hydrated lime. Adapting to different environments, there are other types of lime such as fat or air lime, composed of 95% calcium oxide, or hydraulic lime, composed of clay and ferrous oxide.
Among the properties of lime are its waterproof nature to prevent water infiltration while allowing vapor to pass through to eliminate moisture, as well as preventing the proliferation of mold or bacteria; its high porosity that improves the breathability of the space and helps evaporate moisture from it; its plasticity in mortars that facilitates the placement and adhesion of various materials; its binding capacity that reduces production costs by using waste materials and artisanal manufacturing methods; and its bactericidal action against the development of microorganisms.
Now then, how is the use of lime applied in the contemporary architectural scene? What factors are taken into account when using it in plasters, mortars, and other elements? Until the 20th century, lime was the main binding agent used in housing construction and applied in concrete, mortars, and plasters. Acting as a binder and mixing with other materials such as sand and water, it is commonly used for mortars and concretes in the joining of bricks, blocks, and stones. For example, the House for a Grandmother by Philip Lütken in Denmark features irregular brickwork with thick lime mortar joints filling the spaces. In fact, the lime mortar in the brickwork allows for the future reuse of the bricks.
Lime mortars are dynamic materials capable of interacting with the environment after hardening during the carbonation process and adapting to changes in structures. They have a high level of workability (that is, the proper combination of flow, water retention, and cohesion). Although in very harsh climatic conditions, lime mortars and plasters may not be very durable, this can be counteracted by using hydraulic lime or incorporating Portland cement. Located within a historic district of San Antonio in the United States, the Barrera House by Cotton Estes Architect aimed to apply construction systems and materials that supported resource conservation and low maintenance. The walls were coated with a hydraulic lime plaster.
Considering lime as an ecological construction material and given its significant environmental advantages, the Calx sustainable houses in Peru were conceived. These houses implement reinforced lime blocks in the structural elements and a simple system for the partition elements to optimize and streamline construction. Pezestudio highlights lime's ability to regulate humidity as well as its thermal and acoustic insulation properties, which result in lower energy demand, economic savings for inhabitants, and reduced toxic emissions into the atmosphere.
Additionally, the use of lime in plasters offers a slow setting time and an attractive finish, providing smooth surfaces and lower chances of cracking. It can be applied in the plastering of walls and ceilings, in the preparation of paints and finishes, in soil stabilization, and in improving mechanical properties in the construction of roads and foundations, among other uses. In Mallorca, Spain, lime construction is an ancient technique that, until now, was only used on facades and vertical surfaces. In Natural House, Ideo arquitectura also used it on floors and ceilings, providing an aesthetic and seamless continuity throughout the interior. Meanwhile, in Italy, Studio Andrew Trotter applied a full lime plaster to the interior of Casolare Scarani House with the help of an artisan who makes his lime plasters and paints.
Lime does not require large capital to start its production nor does it need imported technologies or equipment. It can be produced in small quantities for a local market, reducing transportation costs and providing development opportunities for the local industry. Focusing on using local materials and craftsmanship techniques, the walls of the Mud House by Sketch Design Studio, located in Alwar, India, were made with rammed earth using local mud mixed with natural binders such as lime and fenugreek seeds. Additionally, reclaimed stone was used for the walls and foundations, and Bagra, a residue left in lime kilns after limestone processing, was used as mortar for the stone masonry. Indeed, the sustainable construction technique using lime residues has been employed by nearby communities for centuries, and one of the rooms built with rammed earth featured a lime plaster finish, a plastering technique kept alive by a few artisans.
The contemporary use of lime is utilized as a finish in numerous homes extending from Latin America, as in the case of Tatakua House (Paraguay), to Europe, as in Can Bau (Spain). Globally, it has also played an important role in the conservation of ancient buildings and monuments such as churches, castles, and others. Currently, lime is used in glass production, paper manufacturing, agricultural practices, chemical processes, plaster, mortar, and other construction materials. The question is, what will be the future of this material? How will architecture professionals reinvent themselves to make the most of its properties?
Sources:
- Miguel Galván-Ruiz and Rodrigo Rafael Velázquez-Castillo, “Cal, un antiguo material como una renovada opción para la construcción [Lime, an ancient material as a renewed option for construction]".
- Practical Action, The Schumacher Centre for Technology and Development; Lime Technical Sheet.
- Calidra, "2021 Sustainability Annual Report. Sustainable Development".
