Polymer-Modified Cementitious Repair Mortars: A Critical Review of Interfacial Bonding, Curing–Compatibility Relationships, and Durability-Based Selection

Polymer-modified cementitious mortars are widely used to repair concrete. However, favorable properties of isolated mortar specimens do not guarantee durable bonded repairs. This critical review examines how polymer chemistry and delivery form, hydration and film formation, substrate condition, dimensional and electrochemical compatibility, and exposure history jointly control repair performance. Foundational studies are combined with recent work on waterborne epoxy, functionalized acrylate, redispersible powder, and in situ polymerization systems. The reviewed evidence supports formulation-specific benefits, but it does not support a universal optimum polymer content or a general ranking of polymer families, because studies differ in dosage definitions, curing histories, bond-test stress states, and failure-mode reporting. Within-study data show these trade-offs. In one mixture series, 10% SBR reduced water absorption by 75% but compressive strength by 49%. Under sustained loading with seawater wet–dry cycling, a waterborne-epoxy-modified interface lost 30% of its initial tensile bond, compared with 50% for the reference. A four-gate qualification framework linking placement, initial adhesion, retained performance under restraint and exposure, and field robustness is proposed together with a minimum reporting dataset. Thus, repair selection should be based on the performance of the complete repair–substrate system rather than on compressive strength or polymer dosage alone.