Shrinkage-induced cracking in cementitious systems compromises their lifespan and durability. This study addresses concerns related to dimensional variations by examining the diffusion of cement alternatives, including olive waste ash (OWA)—derived from burning the olive oil extraction residue “pomace”— into mortar and cement paste. A comparative analysis is conducted to assess the impact of various OWA levels (0, 5, 10, 15, and 20%) on distinct volumetric stability parameters, namely chemical, drying, and autogenous shrinkage measured during 28 days. All mixtures are prepared using a water-to-cement ratio of 0.45 and a sand-to-cement ratio of 2 for mortar. The results reveal that OWA serves as a key element in reducing all length change parameters, owing to its content and interactions with other components within the matrix. Additionally, mortar specimens exhibit lower shrinkage values relative to paste specimens. Furthermore, the strong correlations between the shrinkage behavior of OWA-based paste and mortar demonstrate that paste performance reliably predicts mortar performance. This paper endeavors to provide valuable insights into the similarities and differences in shrinkage performance of paste and mortar across various OWA levels, optimizing its usage for better sustainable applications.