Salt-Induced Deterioration of Porous Building Materials

Salt-driven damage arises when soluble salts infiltrate the pore network of materials such as stone, brick and mortar. Fluctuations in humidity and temperature trigger cycles of dissolution and crystallisation, generating internal stresses that crack pore walls and weaken structural integrity. Efflorescence and subflorescence phenomena reflect salt migration to the surface or retention within the matrix, respectively, with the latter typically causing more severe damage. Key mechanisms include crystallisation pressure, disjoining pressure within nanometre-scale films and hygroscopic growth under high humidity. Material properties such as pore size distribution, permeability and surface chemistry govern the extent of salt transport and damage. Global interest in this field spans conservation of cultural heritage, durability of modern infrastructure and development of mitigation strategies such as inhibitors, surface treatments and optimised formulations of repair mortars. Advances in imaging, modelling and accelerated testing are improving predictions of long-term performance under realistic environmental exposures.

Research from Nature Portfolio

A seminal microscale investigation measured the forces exerted by growing salt crystals confined within pores, revealing that nanometre-thick wetting films are essential for crystallisation pressure to develop. The study demonstrated that repulsive electrostatic interactions across these films generate the mechanical stress responsible for microcracking and that hydrophobic pore surfaces inhibit film formation and thereby damage. This work provided a quantitative foundation for understanding why different salts and substrates exhibit varied levels of weathering. Emerging efforts are now coupling high-resolution imaging with mechanistic modelling to map stress distribution in complex pore geometries, offering new insights into threshold conditions for damage onset.

Salt-Induced Deterioration of Porous Building Materials publication trend

The graph below shows the total number of articles in salt-induced deterioration of porous building materials across all publications each year (not limited to Nature Index journals).

Technical terms

Crystallisation pressure: The mechanical stress generated when salt crystals grow within confined pores.

Efflorescence: The visible deposit of salts on the exterior surface of a porous material following moisture evaporation.

Subflorescence: Salt crystallisation within the pore structure, often causing internal damage and spalling.

Disjoining pressure: Repulsive force acting across thin liquid films between a growing crystal and pore wall.

References

1. The Pressure induced by salt crystallization in confinement. Scientific Reports (2016).
2. Encapsulated crystallisation inhibitor as a long-term solution to mitigate salt damage in hydraulic mortars. Cement and Concrete Composites (2024).
3. A review of theoretical salt weathering studies for stone heritage. Progress in Earth and Planetary Science (2021).
4. Towards a more effective and reliable salt crystallization test for porous building materials: state of the art. Materials and Structures (2018).