Lime mortar is one of the world’s oldest construction materials. It has a long and rich history from all around the world and can be found in many of the world’s most iconic buildings. At Limebase, we specialise in producing this ancient material and marvel at its use on historic and traditional buildings. Today, we’re going to take a look at the history of lime mortar, focusing on key moments throughout our timeline that changed the game and why it is still used today.
First traces of mortar
Lime, on its own, has been used within the construction industry for over 2000 years. There is mention of it being used in the blends for mortar, internal plaster, external render, foundations and, specifically, for use in moisture-rich environments such as aqueducts. Outside of mud, earth and clay, it is one of the oldest binding materials.
The first mentions of lime mortar are in 6,500 BC in the Indus valley region (present day Pakistan) and later in Egypt on the pyramids in around 2500 BC. Additionally, there are numerous mentions of it being used extensively in the Roman Empire who developed a way to make the entire process more practical. Traditionally, mortars contained only lime and sand. They required carbon dioxide to harden by converting to limestone. This process took a long time. Lime mortar at this time also couldn’t harden if exposed to water or moisture. Roman’s were the first people to develop hydraulic mortars. Here, they blended lime with a pozzolan – possibly volcanic ash or brick dust. This made the mixture harden much quicker and also allowed it to be used in ponds, cisterns and aqueducts.
Key points for lime mortar throughout history
6500 – 4000 BCE – The first mortars contained no lime and were found to mainly contain a mix of mud, clay or sand. These materials were used because of their low cost and general availability. The Ancient Egyptians used gypsum mortars as a lubricant so that the large stones used to build the pyramids could be dragged into place.
4000 BCE – The beginning of the use of lime in mortars is not clear, however the Egyptians found that Limestone, when burnt and combined with water, produced a material that would harden with age. The first documented use of this was when the pyramids were plastered using a lime based plaster.
150 BCE – It is unclear when the Romans started to use lime mortar but by around 150BCE it was a common practice. The Romans developed a hydraulic setting lime mortar with the addition of volcanic ash which is a pozzolan. Vitruvius, writing in around 25BC, specifies a ratio of 1 part lime to 3 parts pozzolan for lime mortar used in buildings and a 1:2 ratio of lime to pozzolan for underwater works.
150BCE – Present Day – Lime mortar continued to be used from the Roman Empire up until around the 19th century where it was surpassed in usage by portland cement mortars. Lime continues to be used today as a more eco friendly building option when compared to cement. Lime is also used to repair traditional buildings which were originally built with lime mortars, this is because lime allows for more movement without cracking or damaging the original masonry. Lime can also be an excellent solution to damp problems as it takes on water and releases it reducing the chances that water will become trapped and damage the building.
Benefits of lime mortar
Although technology has developed new construction products, lime mortar is still widely used. Both for modern and historical homes, it offers a host of benefits that make it highly competitive against alternatives. These include:
- Workability – Lime mortar has a great plasticity. This makes it easy to work with and suitable for shaping into decorative settings. Adding water to lime activates the calcium oxide but does not turn it into a putty or a paste. This means that, during the application, it won’t become slushy causing the immediate area to need additional cleaning.
- Doesn’t separate – Lime is an excellent binder. This prevents the mortar from crumbling away over time, ensuring it can withstand the elements.
- Damp ingress protection – Lime is excellent at protecting your home against damp ingress. This is because lime can take on and release moisture rather than being fully waterproof such as cement based mortars.
- Minimised shrink cracking – Other cement based mortars expand and shrink with temperature, causing the surface to crack. This can spread further as moisture soaks in, eventually leading to crumbling or damage. Lime prevents this from happening and maintains the integrity of your walls.
Why is lime mortar used for historical building restorations?
As a traditional building method, lime mortar is regularly used to repair and restore old, historical buildings. The reasons for these are varied and include:
- Lime mortar is softer than stone or brick, allowing it to accommodate smaller movements without cracking.
- Lime mortar is permeable and allows water vapours through.
- Lime mortar helps to keep a property dry inside without the need for damp proofing courses or chemical treatments.
- Lime mortar is more porous than masonry and encourages evaporation and sale deposition. This protects against the masonry itself decaying.
- Lime mortar can be blended with coloured sands to produce good, matching colour for older buildings.
- Modern, hydraulic lime mortars set quickly and minimise damage to the existing building.
Here at Limebase, we specialise in lime-based products from lime mortars through to lime putty and limewash. Many of our products have been used for the renovation of historic buildings and traditional building materials. We manufacture our own lime putty using lime from Singleton Birch in Lincolnshire and have supplied construction products to major building works including those on Wells Cathedral, Westminster Abbey and Salisbury Cathedral. If you have any further questions about lime mortar, it’s use throughout history, or the ways in which our customers use it today, please get in contact. We’re based in South West England with over 25 years of experience and a friendly team on hand to answer all your questions.