Is Lime Mortar Waterproof?

Lime mortar has been a staple in construction for centuries, renowned for its breathability, flexibility and historical significance. However, one common concern with lime mortar is its susceptibility to water damage.

In South Africa, where diverse climatic conditions pose unique challenges to construction materials, understanding lime mortar waterproofing is essential for preserving heritage structures and ensuring long-term durability. In this blog, we’ll delve into the concept of it from a South African perspective, exploring techniques, challenges and best practices.

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Understanding Lime Mortar

Before discussing lime mortar waterproofing, it’s crucial to grasp the properties of lime mortar itself. Unlike modern cement-based mortars, lime mortar is made from lime, water and aggregates such as sand. It is renowned for its breathability, allowing moisture to escape from masonry walls and preventing issues like trapped moisture, efflorescence and spalling. Additionally, lime mortar offers excellent flexibility, accommodating the natural movement of buildings without compromising structural integrity.

Challenges of Lime Mortar Waterproofing in South Africa

Climate Variability:
South Africa experiences a wide range of climatic conditions, from arid regions in the west to humid subtropical climates in the east. This variability poses challenges for lime mortar waterproofing, as structures must withstand seasonal fluctuations in temperature, humidity and rainfall. In regions prone to heavy rains or high humidity, protecting lime mortar from water ingress is crucial to prevent deterioration and structural damage.

Heritage Preservation:
South Africa is home to numerous heritage buildings and structures dating back to colonial and pre-colonial eras. Many of these structures were constructed using lime mortar, which requires specialized care and maintenance to ensure longevity. Waterproofing lime mortar in heritage buildings presents a delicate balance between preserving historical authenticity and implementing modern waterproofing solutions to safeguard against water damage.

Material Compatibility:
Traditional lime mortar is inherently breathable, allowing moisture to evaporate from the masonry. Introducing modern waterproofing materials such as sealants or membranes can compromise this breathability, leading to trapped moisture and potential damage to the mortar and underlying masonry. Finding compatible waterproofing solutions that maintain the permeability of lime mortar while providing adequate protection against water penetration is paramount.

Waterproofing Techniques for Lime Mortar in South Africa

Hydrophobic Additives:
Hydrophobic additives can be incorporated into lime mortar to enhance its water repellent properties without compromising breathability. These additives create a barrier on the surface of the mortar, preventing water ingress while allowing moisture to escape. However, careful consideration must be given to the type and concentration of additives to avoid adverse effects on the mortar’s performance and durability.

Surface Treatments:
Surface treatments such as lime washes or breathable sealants can provide a protective layer over lime mortar surfaces, reducing water absorption without blocking moisture evaporation. Lime washes, made from slaked lime and water, penetrate the surface of the mortar and form a durable, breathable coating that repels water and resists fungal growth. Breathable sealants, specifically designed for historic masonry, offer additional protection against water infiltration while maintaining breathability.

Proper Maintenance:
Regular maintenance is essential for preserving lime mortar and ensuring its long-term waterproofing performance. Inspecting masonry surfaces for cracks, gaps or signs of water damage allows for timely repairs and preventive measures. Cleaning mortar joints, removing vegetation and addressing drainage issues around the structure can also mitigate water-related issues and prolong the lifespan of lime mortar.


Lime mortar waterproofing in South Africa presents unique challenges and considerations, influenced by climate variability, heritage preservation concerns and material compatibility. By employing appropriate waterproofing techniques such as hydrophobic additives, surface treatments and proactive maintenance strategies, builders and preservationists can safeguard lime mortar structures against water damage while preserving their historical authenticity and cultural significance for future generations.
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