ABSTRACT The environmental impact of Portland cement has led to the exploration of sustainable alternatives in construction materials. This study investigates the potential of olive waste ash (OWA), a byproduct of olive oil production, as a partial cement replacement in mortar. Five mixes were prepared with 0%–20% OWA, maintaining constant water‐to‐cement and sand‐to‐cement ratios (0.45 and 2:1, respectively). The mortars were evaluated for workability, ultrasonic pulse velocity (UPV), compressive and flexural strength, water absorption, and volumetric stability (chemical, autogenous, and drying shrinkage and expansion). Predictive models based on hyperbolic and capillary‐diffusive functions were developed to assess compressive strength and moisture transport behavior over time. Results showed that 10% OWA yielded optimal performance, reducing chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion by 25%, 15%, 21%, and 24%, respectively. At this level, the compressive and flexural strengths were 23.5 and 2.8 MPa at 28 days, representing 24% and 15% reductions, respectively, relative to control. Model predictions correlated well with experimental data ( R 2 > 0.98), confirming the reliability of the findings. This study demonstrates the potential of OWA as an eco‐friendly cement substitute, improving volumetric stability while maintaining structural integrity in non‐structural mortar applications.