Introduction to Lime Mortar Stone Repairs

Scotland has a long tradition of building with stone and lime mortar stretching back to Roman times. A large proportion of Scotland’s buildings constructed prior to 1920 used lime mortars in both construction and finishing.

From the mid-Nineteenth Century, the use of ordinary Portland cement (OPC) mortars became increasingly common. In the Twentieth Century, it became the norm for new construction and became increasingly used to repair traditional builds originally built using lime mortar. This has a negative visual and practical impact and can have a serious effect on the condition of the building.

The construction industry has almost forgotten why lime was used and is having to re-learn the skills to use it effectively.

In the majority of applications, lime has significant performance and visual benefits over cement mortar, particularly in relation to traditional buildings.

Where modern mortars have been introduced into traditional masonry structures, the consequential rate of decay can be alarming.

What is a Mortar?

A mortar is a material in a plastic state which can be trowelled into place and sets in situ. It consists of:

  • A binder (lime, Ordinary Portland Cement (OPC), clay).
  • An aggregate (sand or gravel).
  • Water

Lime Mortar

Lime mortar mixes, whether for building, repointing, harling, rendering or plastering, are essentially made from the same material.

Build lime is produced by burning a naturally occurring form of calcium carbonate (such as limestone, chalk or sea shells) to form quicklime by driving off carbon dioxide. This is done using a kiln and the process was once commonplace across Scotland.

MASONS MORTARS LTD are our suppliers of lime benders and aggregates.

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Lime renders were traditionally applied to give protection to walls built of poor quality rubble stone or porous brick or to walls in exposed locations facing driving winds.

Lime mortar pointing finishes the wall surface and closes the gaps between stone or brick on external walls to keep the surface weather tight. Once finished, the lime mortar pointing acts sacrificially, encouraging the transfer of moisture and salts away from the principal stone and brick construction.

The lime mortar coating known as harling or roughcasting is the most commonly applied external finish to be found on vernacular architecture in Scotland, Edinburgh.

Lithomex lime mortar stone repairs or more commonly known as (the plastic repair) is a repair method we would recommend where surface damage only is evident and the stone element still has its structural integrity intact.

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