Climate change – should lime mortar fill in the gap?

Climate change – should lime mortar fill in the gap? Ashley Pettit, Isle of Man architect and committee member of the Building Limes Forum poses the question.

On September 1st, 2020, it was announced that forty of the world’s leading cement and concrete companies had unveiled a joint industry ‘2050 Climate Ambition.’ The ambition statement demonstrates the commitment of the industry across the globe to drive down the CO2 footprint of the world’s most used man-made product, with an aspiration to deliver carbon neutral concrete to society by 2050.

Research from the Centre for International Climate Research, Oslo, has identified that anthropogenic (man-made) emissions of CO2 to the atmosphere come from three main sources.

1. Burning fossil fuels
2. Deforestation and other land use changes
3. Carbonate decomposition

Cement manufacture is the largest source of emissions from decomposition of carbonates. Manufacture alone, not counting transport, storage, waste and lack of recyclability, is the third largest producer of anthropogenic CO2 in the world – and currently responsible for 65% of all man-made CO2.

But what about in the meantime? Can we wait another 30 years or is there an alternative to cement? The answer is yes – lime mortar! Used successfully for centuries, lime mortar is suitable for modern domestic and industrial buildings.

Image: An office built using lime mortar joints in standard block work and then rendered. 20 years on, it is still standing strong with no movement joints

Lime manufacture involves much lower temperatures and less mechanisation than Portland Cement which results in lower energy requirements and less CO2 produced. Small scale production of lime is not difficult and can be regional, helping to reduce transport distances, energy use and pollution. The lime binder in lime mortars re-absorbs CO2 when the mortar sets, further reducing the total CO2. If sustainable furnace fuel could be used, pure lime mortars and those of low hydraulicity could achieve something close to carbon neutrality.

Image: Kiln for small scale lime burning at Charlestown

So, whilst the 2050 Climate Ambition should be applauded as a monumental step forward in reducing carbon emissions, should we in fact also be shouting about the merits of lime mortar and lime binders which are already helping to reduce carbon emissions and have been for decades? In fact, you could argue that this traditional material meets many of the current aims of the modern built world and could supersede cement in many building activities, for example:

• It is a gentle binder which enables the recycling of building materials.
• It can be used to upgrade old buildings in terms of helping to reduce or eliminate damp instead of them being demolished and rebuilt which increases carbon emissions.
• It future proofs a traditional building skill which creates apprenticeship and employment opportunities.

It is important to remember that the use of lime mortar isn’t just reserved for traditional buildings: there is a great case study where it was used to build an early brick skyscraper 14 storeys high which remains standing and in use in Chicago.

Lime plaster and render assist the evaporation and dispersal of moisture from buildings and lime can be used in foundations. It can also be used as the binder for insulating renders; lime-hemp renders, and other ‘grown’ building materials.

Earth-lime backing coat with hay addition

In conclusion, switching from cement mortars to lime mortars and lime binders for a range of building elements would be a simple yet effective measure to reduce the carbon footprint of construction. So why wait for the magic bullet in 2050 when we could be making that all important difference now?

Next Conference

Looking Back, Looking Forward: learning from the past to inform the future. The Exeter Gathering, originally scheduled for 4-6 September 2020 has been postponed to 27-29 August 2021.

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