Development of a natural surface coating for soil-based materials

Abstract

A coating is a thin film of material applied to a substrate surface to protect against environmental, chemical, and mechanical exposure. Coatings not only enhance surface durability but also significantly prolong the service life of construction materials. Among widely adopted industrial coatings, acrylic and epoxy resin systems are predominant due to their favorable performance profiles. However, growing environmental and economic pressures have necessitated the development of sustainable alternatives derived from renewable resources. Bio-based construction materials are increasingly recognized for their environmental compatibility and socio- economic benefits. Despite advancements, the coating industry faces critical challenges, including escalating production costs, resource scarcity, complex handling protocols, and the toxicity associated with synthetic coating by-products. These concerns underscore the urgent need for non-toxic, environmentally benign, and economically viable coating solutions. Traditional Sri Lankan technologies present a promising foundation, having historically utilized naturally sourced materials such as Dorana oil, Dummala, and plant-derived gums/resins for durable coating formulations. This study investigates the potential of three plant gums: Cashew (Anacardium occidentale) gum, Wood apple (Limonia acidissima) gum, and Pine (Pinus spp.) gum as bio-based binders. Considering their availability and other performance characteristics, Pine gum was selected as the best binder for the coating formula. The final coating formula consisted of Dorana oil, Dummala, Pine gum, and ethanol. Among the formulations evaluated, the composition containing 40 g/L of Dummala and 40 g/L of pine resin exhibited the best performance across key property parameters. This formulation achieved a density of 0.9529 kg/L, a solid content of 55.48% by mass, a viscosity of 21 seconds, an opacity of 10.48%, and a gloss level of 33.5 gloss units at a 60° incident angle. This formula was compared to commercially available synthetic coatings and was found to have similar or superior properties. Furthermore, a sustainability assessment encompassing environmental, social, and economic dimensions was performed to evaluate the feasibility of the proposed formulation. The findings suggest that the developed coating system presents a viable, sustainable alternative for protecting soil-based materials, aligning with the ongoing shift toward environmentally responsible building practices. This research contributes to the field by bridging traditional knowledge with modern material science, providing a foundation for future innovations in sustainable coating technologies.