Benefits of using lime

Lime has been used as a binder for stones and brick and as a plaster or render for thousands  of years. The knowledge of its properties and how to use it has only been lost to current practice in the UK in the last 100 years, other European countries still use lime extensively within construction. Almost all buildings constructed up untill 1900 will have been built using lime, which is still the vast majority of our housing stock. Yet there is now a huge ignorance about lime and its properties. 

Problems of damp and durability associated with the use of cement may not become apparent for many years. English Heritage and  Historic Scotland have banned the use of cement on all historic buildings as it encourages damp and can actually erode the fabric of older buildings that have stood for hundreds of years.                                                                                                                                           

In 1824 Joseph Aspdin a bricklayer from Leeds, England took out a patent on hydraulic cement that he called portland cement because its colour resembled the stone quarried on the Isle of Portland off the English coast, Aspdins method involved the careful proportioning of limestone and clay, pulverizing them and then burning the mixture into clinker, which was then ground into finished cement. It did not begin to be used extensively for another one hundred years.                                                                                                           

Building breathable buildings is a healthier option than building sealed buildings and causes fewer damp problems. Often the waterproofness of cement, coupled with its rigidity and hardness can cause damp and erosion problems. In traditonal stone or brick wall laid with lime mortar, the wall works as a weatherproof surface because the stone keeps the rain out and the lime absorbs the water whilst it is raining and then releases it when it stops. Any moisture that enters the wall either through the mortar or internal plaster will leave the wall once the cause of the moisture stops.                                                                                                                                             

If you replace the lime with cement, you are relying on the cement to make a permanent tight join with the stones or brick to keep the water out. In practice this does not happen because of the rigidity and hardness of the cement, which causes tiny cracks to develop as the wall moves, that allows moisture into the wall. This trickles down inside the wall and then cannot escape because the cement is not permeable, thus creating a damp problem inside the base of the wall. Also water collects at the join between the stone/brick and cement and begins to erode the stone/brick because the stone/brick is often softer than the cement. Many older houses that have been re-pointed with cement show signs of erosion of the stone many years later and suffer damp problems.                                                          

Lime mortars and plasters are 

- Permeable, this means that vapour can pass through them at an almost imperceptible level, which is a healthier option for inhabited buildings as it regulates humidity.

- Flexible, stone or brick laid using lime mortar can move as the earth moves through seasonal weather conditions without cracking the structure or causing instability.

- Soft, plasters and mortars should not be harder or stronger than the background to which they are applied.

- Weatherproof rather than waterproof, thus protecting the building without sealing it.

- Able to control moisture effectively, they can hold excess moisture from the atmosphere in humid conditions without becoming wet. They can then release it back into the atmosphere slowly as humidity drops.

- Proven over centuries, the Romans used lime very effectively in their buildings, including major constructions such as bridges, domes and heated floor slabs.

- Close to being carbon neutral, as over their lifetime, due to the cycle of lime changing from limestone to quicklime and back to limestone again, most of the co2 released during the manufacturing process is re-absorbed during the lifetime of the mortar and plaster.

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