Impact of Moisture-Related Phenomena on the Mechanical Performance and Deterioration of Historic Masonry: A Systematic Literature Review

Historic masonry structures (HMS) are vulnerable to moisture-related deterioration that progressively compromises their mechanical performance and long-term durability. This systematic review synthesises evidence from more than 200 studies on moisture ingress and deterioration mechanisms, salt crystallisation, and freeze-thaw cycling across historic masonry and its components, i.e., units and mortar. Using the PRISMA protocol, research trends are delineated across experimental, numerical, and diagnostic domains. Findings from the review show that, despite methodological advances, the coupled actions of freeze-thaw, salt crystallisation and prolonged wetting remain underexplored, with reported results often showing inconsistent or non-comparable trends across studies. Current research remains fragmented, privileging isolated mechanical parameters with limited cross-scale integration and weak bridges between diagnostics and structural relevance. Priority areas include refining constitutive models and validating links between mechanical deterioration and accessible non-destructive or semi-quantitative indicators, enabling effective calibration of advanced numerical models for conservation practice, alongside recent progress in digital surveying of HMS. The review identifies an urgent need for standardised experimental and in-situ assessment protocols that integrate non-destructive and minor-destructive testing with multiscale and multiphysics modelling. This would enable reproducible, structurally relevant diagnostics, strengthen predictive reliability, and support interoperable diagnostic toolchains, laying the groundwork for consistent, scalable conservation strategies that enhance the resilience and longevity of historic masonry heritage.