Why use a traditional lime mortar for your property?

Lime mortars have been used as a building material for thousands of years.  As recent as the last few decades empirical testing has provided us with a scientific understanding of lime’s remarkable durability. 

Lime has a much lower carbon footprint than cement as it is a natural building material.

Portland cement became more widely used from the 1920’s, prior to this houses were built using lime mortar.  Damp courses were unnecessary as Lime Mortars are permeable, allowing for the transmission of moisture from the inside of masonry to the outside. 

Unfortunately it has become popular over the last 50 years to repoint Lime buildings using cement, which is a non-breathable building material designed for modern houses. Using cement is extremely detrimental as buildings built using a lime mortar need to breath in order to expel moisture. This moisture is what causes extensive spalling and decay of masonry. During the winter time damage is exacerbated by the cold temperatures causing the moisture in masonry to freeze and thaw repeatedly resulting in damage as shown below. 

lime mortar problem in Canterbury

As well as trapping water the cement also forces the water into the interior of the house causing damp issues. This will damage plaster work, rot timbers and has the potential to cause hugely costly structural repairs if left to get worse. Many surveyors will misdiagnose the problem as rising damp  and recommend damp course injections which are an ineffective waste of money.

The solution

The permanent solution to this is to repoint using a suitable lime mortar that will allow the house to breath which will alleviate the damp problem.

Any cracks already caused by the inappropriate use of cement pointing can and must be repaired before being repointed with lime mortar.

If cement mortar is used on lime based masonry it will be incapable of moving in harmony with the rest of the building, as having lime internally and cement externally means the building has two materials very different in their physical properties.

Today slaked lime mortar and mortars made with NHL (natural hydraulic lime) are gaining ground with enlightened architects and contractors, as a better alternative to cement mortar in new builds. These mortars are flexible and much less prone to cracking, whilst the finish they leave is aesthetically pleasing.

Often, buildings were constructed having a “step foundation-footing” base no more than 400mm below the ground. However it is not essential to keep a building constructed with lime mortar rigid. This is because lime mortars can happily move gently over time without cracking.

The mortar should always be softer than the bricks.

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