What does the use of lime contribute to contemporary architecture?

The history of the use of lime in the construction industry dates back thousands of years, spanning cultures and communities globally. In fact, around the year 4000 BC. C., the ancient Egyptians used quicklime mixing it with water as a construction material for their pyramids. Although lime has multiple applications in the food and agricultural, chemical, mining, steel and other industries, in architecture it represents one of the main construction materials due to its versatility, adhesion, impermeability, workability, performance, setting and durability that They allow the production of masonry mortars or mortars, interior or exterior plasters, among other functions.

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Although there are earlier civilizations that have used lime mortars in the development of large structures, the Romans are considered to be the first to use them in construction. More than 3,000 years ago, the Cretan civilization in the Mediterranean used lime as a mortar for masonry while lime mortars were also used on the Great Wall of China. For example, the Pont du Gard aqueduct in Nimes, southern France, was built in 18 BC, being a case of impermeability where mortar based on hydraulic lime was used.

Looking back to the 18th century, Smeaton’s work made it possible to discover the properties of hydraulic lime, which later led to the technology and patent for Portland cement. From the 19th century to the present, the appearance of Portland cement (OPC) produced a great decrease in the use of lime in construction, due to its rapid initial hardening and greater resistance at early ages. However, an appropriate use of lime in construction is capable of involving, among other factors, production with temperatures lower than that of OPC and less energy during its calcination, generating a lower emission of greenhouse gases and a minimum contraction, avoiding cracks.

Being a white powdered inorganic material, lime is obtained from the calcination of limestone, which is a mineral composed of calcium carbonate. Once extracted from a quarry, the limestone is crushed, reducing its size to a maximum of between 80 and 200 mm, and classifying it according to its granulometry. Then, it is calcined at high temperatures (between 900 and 1200°C), causing the release of carbon dioxide and leaving calcium oxide, known as quicklime, as a residue. Finally, the quicklime is moved to storage silos where it is distributed in bags or in bulk. Through the incorporation of 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 by passing the dolomitic quicklime through a hydrator and grinding, pressurized hydrated lime is obtained. Adapting to different environments, there are other types of lime such as fatty 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 leaks while allowing the passage of steam to eliminate humidity, in addition to 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 agglomerating capacity that reduces production costs when made with waste materials and artisanal manufacturing methods; and its bactericidal action against the development of microorganisms.

Now, how is the use of lime applied in the contemporary architectural scene? What factors are taken into account when using plasters, mortars and other elements? Until the 20th century, lime turned out to be the main cementing agent used in the construction of houses and applied in concrete, mortars and plasters. Acting as a binder and mixing with other materials such as sand and water, it is usually used for mortars and concretes to join bricks, blocks and stones. For example, Philip Lütken’s House for a Grandmother in Denmark features uneven brick work with thick lime mortar joints filling the spaces. In fact, the lime mortar in brickwork allows the bricks to be reused in the future.

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 (i.e., the appropriate combination of flow, water retentivity 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, Cotton Estes Architect’s Barrier House sought to apply construction systems and materials that supported resource conservation and low maintenance. The walls were covered with a plaster based on hydraulic lime.

Considering lime as an ecological construction material and taking into account its great environmental advantages, the Calx sustainable houses in Peru were conceived, which implement reinforced lime blocks in the structural elements and a simple system for the partition elements in order to to optimize and streamline construction. Pezestudio highlights the capacity of lime to regulate humidity as well as thermal and acoustic insulation, which produces lower energy demand, achieving economic savings for its inhabitants and lower toxic emissions into the atmosphere.

In addition, the use of lime in plasters has a slow setting and an attractive finish, providing smooth surfaces and lower chances of cracks. It can be applied in the plastering of walls and ceilings, in the preparation of paints and finishes, in the stabilization of soils and the improvement of mechanical properties in the construction of roads and foundations, etc. In Mallorca, Spain, lime construction is an ancient technique that, until now, was only used on facades and vertical walls. In Cáñamo, lime y marés, a natural house, the Ideo Arquitectura studio also used it on the floors and ceilings, providing an aesthetic and plastic continuity of the entire interior, while in Italy, the Andrew Trotter Studio applied it to the interior of the Casa Casolare Scarani a complete plastering with the help of a craftsman who makes his own plaster and lime paints.

Lime does not require large capital to start its production nor does it require imported technologies or equipment. It can be produced in small quantities for a local market, reducing transportation costs and providing development opportunities for local industry. Focusing on the use of materials and craft techniques from the site, the walls of the Mud House by Sketch Design Studio, located in Alwar, India, were made with earth rammed with local mud mixed with natural binders such as lime and fenugreek seeds . Additionally, they used reclaimed stone for the walls and foundations, and used Bagra, a residue left in lime kilns after limestone processing, as mortar for stone masonry. In fact, the sustainable technique of building with lime waste has been used by nearby towns for centuries, and what’s more, one of the rooms built on rammed earth was finished with lime plaster, a plastering technique in force thanks to some few craftsmen.

The contemporary use of lime is used as a finish in numerous homes that extend from Latin America, as in the case of Casa Tatakua (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. Today, lime is applied 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 architectural professionals reinvent themselves to make the most of their properties?

Sources:
– Miguel Galván–Ruiz and Rodrigo Rafael Velázquez–Castillo, “Cal, an ancient material as a renewed option for construction.”
– Practical Action, The Schumacher Center for Technology and Development; Lime Technical Sheet.
– Calidra, “Annual Sustainability Report 2021. Sustainable Development”.