What is Lime Mortar?

Lime mortar is a well known building material dating back over 6,000 years, being used by the Ancient Egyptians in the creation of the pyramids. It’s created by combining both lime and water to make a putty, and an aggregate such as sand or stonedust to create a mortar or plaster. This mortar is then used to bind together the masonry, allowing for the building to be built.

Lime mortar is commonly used in older buildings, being used for thousands of years on many vast architectural projects. Before being surpassed for most buildings to use Portland cement. This said, older buildings that are being restored are not advised to use this type of cement; lime mortar should be used for any restoration or repair work where the building originally used lime mortar.

What is its Purpose?

Lime mortar has been used for thousands of years to hold stone and bricks together to build structures. It’s an easy substance to create and to work with, making it very popular through the years as something to work with and today can be found in many ancient, famous buildings. Today its more commonly used for reconstruction or repair where older buildings that have used a lime based mortar originally. This helps to ensure the structure and allow it to stand strong still.

What Are The Benefits of Using Lime Mortar?

Using lime mortar can bring a range of benefits and should be used in certain situations, such as if restoration or repair work is being conducted on a building that originally used lime mortar. Other benefits are included below:

It’s Nearly Carbon Neutral

The process of creating lime mortar its nearly carbon neutral, whereas cement production creates around 1.25 pounds of CO2 per pound of cement. This makes lime based renders, plasters, and mortars more environmentally friendly.

Cracking and Building Movement

By using a lime mortar, this helps the building to withstand natural movement that it will experience. Commonly buildings expand and contract through the varying temperatures that it faces, which can cause cracks to build and damage to appear over time. Incorporating a lime mortar allows any micro-cracks to repair themselves naturally, with the lime infusing into the small cracks and then hardening to form calcium carbonate (limestone), resolving the crack.

Water Insulation and Frost Resistance

Because of the lack of large cracks as said above, lime mortar effectively keeps any water, such as rain, out of areas that it shouldn’t be. This works for frost resistance too, as it’s much more difficult for water or frost to get into any small cracks or gaps, it allows the mortar to become effective at preventing damage from water or frost.

What Are The Different Lime Mortar Products Available?

There are three known products that are used in construction for various reasons, such as:

Hydraulic Lime

Hydraulic lime is the more commonly used due to the fact less material knowledge is required to use it effectively and is the difference between the three products, where it sets by reacting with water and CO2 in the air. It’s created by using either naturally formed rock or from a mixture of hydrated lime and reactive binder components.


Quicklime will usually be ‘slaked’ to form a ‘lime putty’ which is then matured before use in either a mortar, plaster or render. It reacts with the CO2 in the air to set and harden. It is sometimes used to produce ‘hot lime mixtures’ but is more commonly ‘slaked’ to produce a ‘lime putty’, these are both products that are commonly used in restoration work on older buildings and in new buildings too. The beauty of this product is that it can be pre-mixed and can be stored in airtight packaging indefinitely, and will improve with age.

Hydrated Lime

Hydrated lime is commonly used as a plasticiser for cementatious mortars, it is not advised to use hydrated lime on restoration work.

Famous Buildings That Use Lime Mortar

Throughout history, people have used lime mortar to create some truly amazing structures. Below are a few examples of buildings that are built from lime mortar.

The Great Pyramids of Giza

Our ancient Egyptian ancestors built the famous pyramids using lime mortar as a binder and to plaster them as well as incorporating lime mortar in their homes and their religious temples.

Roman Empires

During the Roman era, the empires were built using lime based mortars extensively. A famous Roman, Vitruvius, was a Roman architect who wrote some basic guidelines on the appropriate mixture of lime mortar.


An Indian structure standing for over 4,000 years is a monument of the Indus valley in Pakistan, it was built using a lime based mortar.<

What Other Differences Does Lime Mortar Have Compared to Cement?

Lime mortar often takes a lot longer to fully set than cement; cement often reaches its full hardness within a month whereas lime mortar can take longer to fully harden and set. This makes cement a popular choice for modern buildings, as the cement is able to harden quicker and reach its peak hardness in a much shorter amount of time.

Lime mortar is often much easier to work with therefore allowing it to be used in reconstruction, repair or new building work with greater efficiency.

Cement is a very hard substance, which although sounds great it can sometimes mean it’s too hard for the substances that it works with and can cause cracking. Lime mortar is softer and can help prevent cracking by allowing tiny movements within the building, with micro-cracks being able to heal themselves to prevent further problems from water or frost down the line.

Cement is waterproof, allowing for a complete seal to prevent water leakage, this can sometimes cause damp problems due to the trapped water having nowhere to go, lime mortar however does not do this. Lime mortar is breathable, meaning it takes on water and releases it, reducing the chances of damp problems and trapped water issues common with cement. This allows it to be safely used on buildings without any sealing in conjunction to its self-healing properties (in some cases excluding hydraulic lime mortar), allowing for any micro-cracks to be resolved by itself which prevents any further problems that could potentially have been created by frost or colder temperatures.

Lime mortar is permeable, allowing for a vapour to pass through it at an almost negligible level. This makes it benefitial for all building types, as it can help to regulate humidity, which cement cannot as it does not permit vapour passage.