Lime-Based Mortars in Historical Conservation

Lime-based mortars have underpinned building practice for millennia, valued for their compatibility with masonry heritage, permeability and modest mechanical strength. Formulated from air lime or hydraulic lime binders combined with aggregates such as sand or crushed stone, these mortars harden chiefly through carbonation and, in the case of hydraulic varieties, through limited hydraulic reactions. Their low elastic modulus and capacity to accommodate differential movement render them ideal for repointing joints, rendering historic façades and reinstating lost plasterwork. The inherent porosity of lime mortars permits moisture transport, reducing salt accumulation and freeze–thaw damage in porous substrates. Contemporary research has refined mix designs to match the original mortar’s texture and strength, incorporated pozzolanic admixtures and evaluated the impact of environmental exposure. Conservation specialists now balance traditional recipes with performance testing under realistic curing regimes, ensuring long-term durability without compromising authenticity. Increasing attention to the global carbon uptake of lime materials spotlights their role in sustainable restoration. From medieval cathedrals to vernacular dwellings, lime-based mortars continue to offer a versatile, reversible and low-impact solution for the preservation of historic masonry worldwide.

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Lime-Based Mortars in Historical Conservation publication trend

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Technical terms

Lime-based mortar: A blend of lime binder (air or hydraulic) and aggregates that sets and hardens primarily by carbonation and, in hydraulic forms, by limited hydration reactions, used for masonry repair and rendering.

Natural hydraulic lime (NHL): A lime binder containing clay impurities that imparts hydraulic setting properties, enabling partial strength gain under water or high humidity.

Carbonation: The chemical reaction between calcium hydroxide in lime mortar and atmospheric carbon dioxide, forming calcium carbonate and driving hardening.

Pozzolanic reaction: The reaction of reactive silica or alumina materials (pozzolans) with calcium hydroxide in lime to form additional cementitious compounds, enhancing strength and durability.

References

1. The effect of lime addition on weathering resistance and mechanical strength of gypsum plasters and renders. Cement and Concrete Composites (2023).
2. An investigation of the global uptake of CO2 by lime from 1930 to 2020. Earth System Science Data (2023).
3. RILEM TC 277-LHS report: a review on the mechanisms of setting and hardening of lime-based binding systems. Materials and Structures (2021).
4. RILEM TC 277-LHS report: lime-based mortars for restoration–a review on long-term durability aspects and experience from practice. Materials and Structures (2022).