Bio-Based and Mineral-Derived Fibres for Mortars: A Review of Performance, Durability and Engineering Applications Across Binder Systems

Natural fibres, both bio-based and mineral-derived, are increasingly investigated for use in mortar as a means of improving technical efficiency while potentially reducing reliance on synthetic fibres where performance and durability are adequate. This review synthesises mortar-focused evidence across cement-based binders, air lime and natural hydraulic lime binders, gypsum-based binders and clay-based binders, with emphasis on mix designs, fibre–matrix interactions, durability-related behaviours and engineering applications. Across binder systems, the most consistently reported benefit of fibre incorporation is improved crack control and post-crack integrity, provided that fibre dispersion, dosage, and workability are adequately controlled. Some formulations also exhibit reduced measured drying shrinkage, whereas changes in compressive and flexural strength are inconsistent, reflecting the effects of fibre type and content, water demand, density, pore structure and matrix–fibre bonding. Durability is strongly binder- and exposure-dependent. For cement-based mortars, alkaline and calcium-rich pore solution remain key limits for many plant fibres, especially under wetting–drying exposure. For lime-based, gypsum-based and clay-based mortars, chemical attack is generally less severe, but performance and property retention remain sensitive to moisture history, curing path and conditioning. Hygrothermal and hygric effects are conditional and should be considered alongside density, moisture state, pore structure and water uptake. Overall, natural fibres are most convincing when crack control, post-crack integrity, compatibility or moisture-related performance are required, rather than for universal strength or durability improvement. For that, further studies and optimisation are needed.