Lime Mortar Design: The Original Expansion Joint

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Lime Ribbon Pointing on Bluestone. Not only used for it’s aesthetic properties, lime mortar allows for flexibility within the stone building.

Lime Mortar has been used for over 6000 years. The pyramids of Giza are plastered with it. Castles throughout the world, buildings of all size and stature, all share one thing: lime mortar. Typically generated through the decomposition of seashells early on, the process of ‘slaking’ limestone by way of kiln/fire came about at a later stage.

As it was noted for it’s inherent abilities for adherence and flexibility, lime mortar has not only been used in stone building in order to bond stones together within the wall matrix but it also serves as an expansion joint; allowing for movement within the wall without destroying the stone itself. The following picture indicates natural deformation of a bluestone masonry wall where settlement or foundation failure has occurred to a minor degree.

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Foundation failure is common in old stone buildings. Without concrete footings, these stone buildings generally relied on larger stone (ballast) placed directly on top of natural soil.

With this inherent movement capability, lime mortar design is a key factor in the restoration, conservation and preservation of these buildings.

In relationship to mortar’s cementitious (cement/ oxide) component, lime, when used in traditional mortar mixes for laying and pointing stone, should always outweigh the amount of cement used.

Lime is still used in today’s concrete design as a plasticizer although chemical dispersants are becoming more predominate as they are more cost effective.

 

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