A brief history of lime mortar

Ancient Egyptians were the first to use lime mortar in the pyramids at Giza around 4,500 years ago; it was also incorporated into their temples and homes. Through the centuries it became more frequently used in construction around the world. However, with the introduction of Portland cement during the 19th century, the use of lime mortar declined. This was largely due to cement’s ease of use, its quick setting nature, and high compressive strength. The negative effects of doing this were not widely understood at the time - cement was seen as a quick and cheap solution to the problem of old pointing. The soft and porous properties of lime mortar provide many advantages when working with natural stone, terracotta and brick that have only recently been fully understood.

Lime mortar does not adhere as strongly to masonry as Portland cement. When cement reaches the end of its life, it often pulls away some of the masonry causing irreversible damage and seriously affecting on the look of the property. Many buildings now have decaying stone or brick on their facades as a result, examples of which can be seen in our Rogues Gallery**.

Portland cement irreversibly breaks under stress, whereas lime produces microcracks. Through the magic of chemistry, these microcracks recrystallise, effectively self-healing the affected area.

Buildings constructed prior to 1910 tend to have been built with relatively shallow foundations - minor movement in such buildings is common. This movement breaks the weakest part of the wall, and with Portland cement as the mortar this is usually the masonry itself. When lime mortar is used, the lime is the weaker element and the mortar cracks in preference to the masonry. This results in much less damage, and is relatively simple to repair.

Cement is much less porous than brick, so damp is retained within the building. Lime, on the other hand, is more porous than cement, brick and stone, and wicks any dampness in the wall to the surface where it evaporates. This is referred to as 'breathability'. Degradation of the stonework and the overall structure is due to damp being trapped within the walls of the building. This can be countered by the use of lime mortar.

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Despite its use over millennia, lime mortar's effectiveness as a building material was not well understood. The practice of using it was based on tradition and folklore, vindicated by the vast number of old buildings that remained standing. Only during the last few decades has scientific testing provided a clear understanding of its remarkable durability, benefits and practical value.