Development and Performance Evaluation of a Bio-Based Fire-Retardant Coating Derived from Eggshell, Oyster Shell, Wood Ash, Rice Husk Ash, Cornstarch, and Sodium Silicate

This study investigated the development and performance evaluation of an eco-friendly fire-retardant coating for wood surfaces formulated from eggshell ash, oyster shell ash, rice husk ash, wood ash, cornstarch, and sodium silicate. Previous studies have demonstrated that calcium carbonate–rich shell wastes, such as oyster and eggshells, can significantly reduce flammability and delay ignition when applied as fire-retardant coatings for wood materials (Dusaran, 2024; Atienza & Cruz, 2021; Wang et al., 2021) [20, 6, 60]. In addition, silica-rich rice husk ash has been reported to enhance fire resistance by forming a protective thermal barrier during heat exposure, particularly when combined with biodegradable binders (Breboneria et al., 2023; Basri et al., 2021) [14, 10]. Natural polymers such as starch have also been identified as effective intumescent materials capable of forming char layers that limit flame propagation (Carvalho et al., 2023) [15]. Despite these findings, limited research has explored the combined use of multiple waste-derived ashes and bio-based binders in a single sustainable fire-retardant coating formulation.

An experimental research design was employed using three coating formulations with varying material ratios, which were applied to wood samples and compared with an untreated control. Fire-retardant performance was evaluated based on flame spread, flammability, and time-to-ignition tests conducted under controlled conditions. The results showed that all treated samples exhibited improved fire resistance compared to untreated wood. Among the formulations, Sample 2 demonstrated the most effective performance by delaying ignition for up to 190 seconds, preventing flame spread (0.00 cm), and exhibiting self-extinguishing behavior, whereas the untreated sample ignited within 50 seconds and showed rapid flame propagation.

The findings confirm the synergistic fire-retardant effects of calcium-based shell ashes, silica-rich rice husk ash, and the intumescent behavior of cornstarch within a sodium silicate matrix. This study concludes that the developed multi-ash coating presents a viable, low-cost, non-toxic, and environmentally sustainable alternative to conventional synthetic fire-retardant coatings while promoting waste utilization and enhanced fire safety for wood-based materials.