The durability of concrete structures is compromised by the presence of cracks, which can lead to further deterioration if left untreated. To prevent this, it is crucial to close the cracks and restore impermeability. This paper proposes an economical and practical solution: the application of biopolymers as an external treatment layer on horizontal concrete surfaces to seal cracks. The study explores the crosslinking of calcium alginates and gelatin at various concentrations. Several properties are investigated, including water permeability, freeze-thaw resistance, overall visual degradation, resistance to chloride intrusion, and adhesive strength of the repair layer. The findings indicate that repair layers utilizing calcium alginate demonstrate promising results for external crack sealing applications. These layers effectively restore impermeability, exhibit resistance against chloride intrusion, improve freeze-thawing resistance, while showing an acceptable adhesive strength to the horizontal concrete substrate. This suggests a viable solution for enhancing the durability of concrete structures.