Frequently Asked Questions, General Installation Guidelines, Information

Lime Mortar vs Portland Cement

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.

9 thoughts on “Lime Mortar vs Portland Cement

  1. Robert Johnson says:

    as a regular proponent of lime, often trying to encourage architects and engineers, I would love this article to be referenced. breathability, flexibility, embodied carbon, and self healing.
    Thank you for all the work you do!

    1. Anthony (LimeWorks) says:

      You are always welcome to share any of our blog articles freely with whomever you feel they would best benefit! All we ask is that you not reproduce the article in full somewhere else without permission and for any quotes or references to the post, please cite us as the source with a link to this article. If we can help you further, please feel free to get in touch.

    2. Joseph Ekuma says:

      I see lime is good

  2. Robert Schlundt says:

    I want to construct a 8x4x4 cold storage. I have a area that’s is always damp but never wet and always shaded. My plan was to drop it 1 foot below grade and access thru a side door and pour a solid top bottom sides.. been vasselating between doing a lime pour for entire project or block with lime motor and plaster with a lime floor.. any thoughts,

    1. Anthony (LimeWorks) says:

      Hello Robert, given how specific your question is, I’m going to email you to talk more about it. I need a bit more information before I can weigh in.

  3. David says:

    I am repointing my stonewall. I have cleaned out most of the old cement, leaving spaces 1/2 in to 21/2 in wide and 2in deep. I like the idea of using lime morta, but I am a little hesitant on the lime sand mix ratio. Your thoughts please.

    1. Anthony (LimeWorks) says:

      Hello David. Generally, you’ll want a 1 part lime to 2-2.5 parts sand. For larger joints, you may want to err towards the 2.5 parts sand. For those large 2.5″ joints, you may also want to consider using a concrete sand instead of a mortar sand. The concrete sands have a coarser particle size which can help prevent shrinkage cracks. For joints up to about 1.5″, a normal masonry sand or all-purpose sand should do the trick. Please feel free to reach out to our team directly if you’d like to talk more about your project.

      You may also find our General Installation Guidelines useful: https://www.limeworks.us/product-documents/#1570047876744-c3488895-5af4

  4. Emily says:

    I found your company through the this old house guy post on mortar and what to use with old houses. I’m stuck in between years in when Portland mortar would have started being used but lime used too. House was built in 1926. We are located outside Chicago IL and have a red scratch brick house with what used to be charcoal mortar, it’s breaking out at the water table and where bad old masonry work was done on our front porch.Its also black at the top still but turns lighter where the elements have hit it. I have them starting the grinding but now I’m bm not sure what mortar to pick to preserve our old house, I wish I would have found your website before I had them start the work. They said they do S or N and I’ve seen their work on other old buildings in our area is done well… but I worry -S may be too strong for our brick. I am finding little to no information on scratch brick which is not the same as Chicago common brick which is very soft and more often used in our area than scratch brick… our brick has no holes in it, it is solid. Thank you for your support!

    1. Anthony (LimeWorks) says:

      Hello Emily. In your area at that time, cement-lime and cement-only mortars were more common than lime-only mortars but the further you are outside the city, the more likely a lime-only or lime-rich cement-lime mortar becomes. Unfortunately, without seeing a sample of your historic mortar in person or knowing the properties of your brick, I cannot give you a definitive answer on what mortar is appropriate. In general, Type S is very frequently too dense and hard for historic brick, so if the choice is between N and S, I’d usually recommend you err towards the softer Type N. However, Type Ns can also be too hard for historic brick. You can do some basic tests like a scratch test and absorption test to get a sense of how resilient the face of the brick is. If a face is easily able to be scratched with, say, a steel key and a little spritz of water absorbs rapidly into the surface, you probably want to avoid cement-lime mortars harder than a Type O (the next step down from Type N) and would maybe even want to consider a lime-only mortar like an NHL 3.5.

      Please feel free to reach out to me directly by phone or email if you’d like to discuss this more.

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