However, Lime is a versatile material in constructing buildings that can be used as mortar in masonry systems and home foundations, offering structural strength and environmental benefits. Below, we look at why opting for lime-based mortars as an alternative to cement and concrete for our home foundations can reduce the carbon footprint of our homes.

The Lime Cycle 

Limestone is one of the most abundant materials on Earth. In the United States, crushed limestone made up 68 percent of all crushed rock produced in the United States in 2007. While limestone is one of the key ingredients in the production of Portland cement, its use predates the cement industry by thousands of years. Architects during the Roman Empire used lime mortars mixed with volcanic rock to build impressive structures (such as the Colosseum) that continue to stand today.

Hydrated lime, or the quick lime used for construction purposes, is formed by burning sources of calcium carbonate (CaCO3), also known as limestone (or occasionally magnesian limestone). The burning process requires high temperatures between 850°C and 1200°C, which forces carbon dioxide out of the limestone (and into the atmosphere) to create calcium oxide (CaO, or quicklime). The calcium oxide is then slaked with water to produce calcium hydroxide eventually (Ca(OH)2) used for construction purposes. While lime also requires burning in ovens at high temperatures, lime requires less energy to produce than cement due to lower temperature requirements.

While building lime does release carbon dioxide into the air during the burning process, lime products can absorb the carbon dioxide in the atmosphere through a process known as the lime cycle. The lime cycle begins when limestone is burned and releases CO2 into the atmosphere. The slaking process eventually creates calcium di-hydroxide, which is sold as a bagged lime powder. This can be mixed with sand or other coarse aggregate and water and used as a more natural mortar (and plaster) alternative. As the mortar hardens, it reabsorbs the carbon dioxide in the atmosphere and eventually re-hardens into limestone. Through this cycle, lime is widely considered a carbon-neutral building material, as it reabsorbs the carbon dioxide released during the manufacturing process.

Lime is a much more environmentally friendly building material because it is biodegradable and can be removed, re-wet, and re-mixed. On the other hand, concrete is rarely recycled and ends up choking landfill sites around the country. Due to its relative flexibility compared to concrete, Lime can also accommodate structural movement as homes settle, thus avoiding structural foundations cracking that can lead to condensation and moisture issues.

Using lime for plasters and mortars can also help to improve the indoor air quality inside our homes. Unlike cement, lime can absorb and release moisture, thus helping to prevent condensation, the leading cause of molds and mildews affecting households around the country. Also, foundations that use lime mortars will not need expansion joints, whose sealants often deteriorate and lead to moisture problems. Lime is highly alkaline and, therefore, naturally antibacterial, antifungal, and antiseptic.

On top of a rubble trench, a solid rock stem wall works exceptionally well with lime mortars. It is a much more durable, natural, and aesthetically pleasing option for a home foundation. According to the American Society of Home Inspectors article, “lime mortar sets in several hours, but the final hardening is a prolonged process as the lime re-forms into calcium carbonate. This can take months or years to achieve maximum strength. The result is a mortar that expands slightly as it sets (making shrinkage cracks unlikely) and relatively stable through temperature changes. Lime mortar is also porous enough to allow water vapor to migrate out of the masonry and water-soluble enough to enable it to redeposit itself and ‘heal’ hairline cracks that appear due to settling or other stresses.”