While lime may conjure up images of tropical drinks and zesty fruit, it is also a green material that has been used in construction for centuries. Lime mortar is eco-friendly and meets energy performance targets, making it an ideal choice for modern building practices.
In a world where protecting the environment is a key priority, using materials that have a minimal impact on the earth is crucial. Lime meets these standards and has been employed as a building material for millennia.
The use of lime in building construction can be traced back to ancient times. It was used as a binding material for timber, earth and stone, making structures more durable and effective. It’s safe to say that when lime was first used, concerns about climate change caused by burning carbon-based fuels were not on anyone’s radar.
However, as industrialisation started to have wider environmental effects, carbon emissions and climate change issues became more pressing.
Despite this, lime remains a popular and sustainable material for building construction, with its ability to mitigate the environmental impact of carbon emissions making it an attractive option for builders and architects alike.
Go green!
The manufacturing of limes or hydraulic limes (HLs) has been found to result in less energy consumption and fewer greenhouse gas emissions compared to the production of Portland cement per unit weight.
While it’s true that the production of binders from limestone requires considerable energy input, binder producers are continuously working to reduce their energy usage and carbon dioxide emissions. They are achieving this by switching from hydrocarbons to other fuels and adopting more efficient production processes.
The total energy used per tonne of lime-based mortar can be between 75 and 90% lower than that of cement-based mortars. Furthermore, lime-based mortars have the added advantage of absorbing most of the carbon dioxide that is emitted during the calcination process over time, while cement-based mortars do not normally have the same level of re-carbonation.
Unlike cement, lime continues to absorb carbon dioxide, reducing the amount of CO2 released into the atmosphere throughout its functional lifespan.
Lime is created by heating materials like limestone, shells, and chalk in a kiln, releasing carbon dioxide and producing calcium oxide. The calcium oxide becomes calcium hydroxide or lime putty when mixed with water. It is then used as a binder for mortar and plaster, setting via a chemical reaction called carbonation.
The carbonation process effectively turns the calcium hydroxide back into calcium carbonate, the same material extracted from the quarry. As it cures, the carbon given off during the kiln process is reabsorbed, ultimately reducing the carbon footprint of building projects.
This natural lime cycle is a great reason to choose lime over cement. This makes lime an excellent choice for those looking to reduce their carbon footprint while still building strong and durable structures.
Think tradition
As we strive to build sustainable and long-lasting structures, traditional masonry techniques such as hot lime pointing have seen a resurgence in popularity.
The use of lime mortar instead of cement not only creates a more durable structure but also allows for better breathability and flexibility in the face of changing weather conditions. This is especially important in regions like Yorkshire, where the weather can be particularly harsh.
Lime mortars are essential components of many historic structures, and they withstand the test of time. Interestingly, because lime can be cured through carbonation, it can be recycled, offering an eco-friendly and cost-effective solution for construction projects.
The process involves using old lime mortars as aggregates alongside fresh lime to create a new and effective mortar mix. Fresh lime is crucial in this process, as old lime has already carbonated and wouldn’t do well in binding the aggregates.
By using such a recycling technique, the authenticity of the structure can be maintained while reducing the need for fresh aggregates like sand to be quarried.
This innovative approach also helps decrease emissions. So next time you need to undertake hot lime-pointing repairs, consider recycling old, decaying mortars to create a new, durable mortar mix.
The Lime Buildings Forum notes the value of lime in various ways, not least the ecological. Under that heading, it highlighted the fact that it contains less embodied energy than cement. It also absorbs carbon dioxide in the process of carbonisation, locking it away. Thirdly, lime can be produced on a small scale, which uses less energy.
Apart from this, it noted, the fact lime has “gentle binding properties” means it makes it simple to reuse other materials in conjunction with it. Clay soils can also be stabilised by low quantities of quicklime and in small amounts it can protect “very low energy materials” like earth construction and straw bales.
Sustainability
When it comes to environmental concerns surrounding building materials, embedded concrete is a major culprit for its potential to contaminate the environment when demolished.
However, lime mortar is a highly sustainable alternative that not only avoids such impact, but is also known for its durability. It has been the go-to choice for many successful restoration projects, ultimately eliminating the need for demolition altogether.
We recommend checking the video by Historic England on the topic of embodied carbon and the case against demolition. Please view it here.
What’s even more impressive is that old lime building materials can be reused to create new ones, making lime a highly cost-effective and eco-friendly option. Moreover, as lime is biodegradable, it naturally disintegrates into calcium carbonate, which can be found in natural rocks like limestone and chalk.
Unlike cement, lime does not produce any toxic by-products during construction. Even after its use, lime can still be utilised to improve soil quality by being crushed and spread over gardens to help reduce acidity and increase soil aeration.
In the long run, lime is not only an excellent choice for builders and environmentalists alike, but for the health of our planet as well.
Climate change
As our climate continues to change and sea levels rise, buildings are increasingly at risk of flooding. The good news is that lime mortars offer a solution to combat this threat.
Not only do they wick moisture out of buildings, allowing them to dry faster, but studies at Sheffield Hallam University have shown that traditional solid wall constructions can prevent water ingress and stay much drier than modern cavity wall systems.
Cement mortars and renders set with micro-cracks, allowing water to penetrate and ultimately damage the building. However, the complex pore structure in lime mortars can help prevent water ingress, making them a better choice for buildings located in flood-prone areas.
By using lime mortar, we can help protect our homes and buildings from the damaging and costly effects of water damage.
When it comes to choosing materials for construction and decoration, it’s important to consider not just their aesthetic appeal but also their impact on the environment.
Cement mortars, gypsum plaster and plaster boards may seem like convenient options, but they come with a drawback: they trap moisture in behind them.
Once the gypsum plaster and plasterboard become saturated, they have to be replaced, which leads to more waste and further harm to the environment. In contrast, historic lime plaster is highly porous and actually supports substrate drying. While some may be tempted to remove it from surfaces, this is rarely justified.
Permeable coatings such as lime-wash are becoming increasingly popular in the realm of sustainable living. By using this traditional technique, surfaces can be decorated even when damp without causing damage. Not only is this practical, but it also takes into consideration the impact of modern paints on the environment.
VOCs, the hazardous environmental impact of paints, are released during the drying process of modern paints, making them a significant risk to the environment.
Paint disposal also needs to be undertaken properly, if not it can have a huge effect on the environment through the introduction of toxic waste. By switching to permeable and natural coatings like lime wash, we can reduce this risk while still allowing walls to dry. This is a small but important step in creating a sustainable future for our planet.
