Lime Mortar vs. Portland Cement

Both pure Lime-based mortar and Portland Cement-based mortars have widespread use in construction. Portland cement and lime mortar possess different attributes for various applications. In this discourse, we will explore the disparities between these materials, their merits and drawbacks, and their optimal application scenarios.

Lime Mortar

Lime Mortar, an age-old building material, amalgamates lime, sand, and water and is often employed in restoring historical edifices. Lime Mortar offers numerous advantages over Portland Cement Mortar, including:

• Breathability: Lime Mortar fosters moisture permeation, curbing dampness intrusion into interior finishes by allowing moisture to pass to the outside atmosphere rather than rotting in the core of mass wall masonry systems. As a benefit to this, it then promotes superior indoor air quality because the building breathes. It can be used as an interior plaster system and as an exterior sheltering render for the vertical walls of the building envelope. On a larger scale, its moisture re-release capacity proves pivotal in flood-prone areas, minimizing prolonged harm.
• Flexibility: Lime Mortar accommodates building vibrations and slight structural shifts, which minimizes cracking. Lime Mortar has a higher modulus of elasticity than the brittleness of Portland cement-based mixes. This ability to deflect and recover also enhanced fracture resistance. In seismic zones, its malleability aids during tremors and has proven that the lime mortar-built structures of hold often hold up in these conditions better than their rigid-built modern structures that utilize higher strength, less yielding, and dense Portland Cement base mixes.
• Durability: Despite naturally being softer than Portland cement mixes, Lime Mortar, when correctly applied, endures for centuries because it is not in conflict with slight movements of the earth and the vibrations of buildings and because it works symbiotically with water to take it in and re-release water in a perfect manner of conductivity. Although naturally possessing a lower strength than Portland Cement-based mixes, Lime Mortars can be adjusted or modified with clean pozzolans that can help it gain appropriate structural strength to build many stories, as is evidenced by most all grand historic masonry buildings constructed in the US before 1870 that are still in service and working.
• Self-Healing: The proper amount of Free Lime content allowed to remain in well-crafted limes facilitates autogenous healing of the Lime Mortars. “Available Lime” is another name for Free Lime which is lime not fully carbonated within a mortar mix. This Free or “Available” lime can go into solution when a fissure opens, and water is driven to activate it to a crystalline bridge across cracks that might open up.
• Eco-Friendliness: Lime production demands significantly less embodied energy than manufacturing Portland cement. With lime emitting over 80% less CO2 in manufacturing, lime is a natural, environmentally benign alternative to use as a binder in mortars, plasters, and stucco. It is imperative in the current times to use Portland Cement only when and where it is needed and not for every mortar or stucco need.
• Salt Resistance: Lime is immune to sulfate attack. Ordinary Portland Cement has a byproduct that causes it to react with salts known as Tri-calcium aluminates. A high-quality lime mortar will be devoid of this, and therefore, when salts from ocean mists or from within the core of all old walls where weak carbonic acid forms sulfate, Lime Mortar is not negatively affected by its presence in these conditions.

Portland Cement

Modern Portland Cement comprises limestone, clay, and gypsum, serving construction purposes, notably in concrete production. Portland Cement boasts several advantages over Lime Mortar, such as:

• Strength: Portland Cement excels in strength, supporting substantial loads, making it apt for bridges, roads, dams, and skyscrapers.
• Rapid Setting: Portland Cement exhibits swift curing for time-sensitive construction endeavors.

However, Portland Cement also bears drawbacks. It naturally lacks breathability because it is so dense. It fosters dampness and a cold and clammy feeling rather than superior indoor air quality and comfort discovered when using Lime Mortar and a complete lime-based building system. Portland Cement lends to the potential for the decay of adjacent building elements. It negatively reacts with salts, allowing salts to corrode the steel that supports it. It does not return to the earth like Lime Mortar but causes the excessive need to landfill it after planned demolition. Moreover, it’s prone to cracking with structural shifts, therefore problematic in seismically active regions, and flood conditions do not quickly dry out as Lime Mortars do. Finally, the carbon footprint of Portland Cement is so much greater than that of lime in production that the world should seriously consider that it should be used only in approved engineered applications.

LimeWorks.us Ecologic™ Brand Lime Mortar, Plaster, and Paint have many superior applications that substitute Portland Cement as the binder for the appropriate corresponding application. Call us to find out which of our products would suit your upcoming project, whether a Historic Masonry Restoration or a Sustainable New Building.