This research examines the physico-mechanical properties of soils amended with psyllium husk, a commercially available plant-polysaccharide-based soil stabilizer, used as a biological amendment and sustainable alternative to synthetic amendments for soil-based shelter coats. Common to all raw-earth-based construction, local availability, low cost, and low environmental impact are important aspects; however, earth is also highly sensitive to moisture. The increasing intensity of a single rain event due to climate change thus threatens the viability of earthen heritage in traditionally arid areas. For over 5 decades, synthetic organic polymers have been used to amend earthen materials; however, the success of these materials depends on the composition and moisture content of the soils. Incompatibility, irreversibility, and low sustainability further prompted reconsideration for alternatives to cope with diminishing resources and a changing climate. Among the possible alternatives are biological materials. With roots in traditional building practices, biological materials have been recently researched to reinforce soil in infrastructure and agronomy. Lab-engineered materials provide promises for artificially controlled quality beside environmental-friendliness. This research emphasizes two aspects of biological materials: water damage resistance and wide availability and low cost for immediate implication of site implementation. Psyllium husks are selected for further evaluation through laboratory-based testing designed for the desired properties. X-ray diffraction and SEM-EDS analysis shed more light on soil clay mineralogy and soil microstructure. Overall, psyllium husk presents high capacity in improving the resistance and durability of shelter coating materials against water-related damages. Further research on both psyllium husk and other biological materials is embarked.