Abstract: To address the aging issues of intumescent fire-resistant coatings, which are the most widely used for steel structure fire protection, a simple natural weathering test site was established. A total of eight coatings，comprising water-based and solvent-based types from two representative domestic and two international brands，underwent a natural aging test lasting up to four years. The aging behavior of the conting was systematically characterized through visual monitoring, fire resistance testing, element analysis infrared spectroscopy, etc. Results demonstrate that outdoor exposure significantly accelerates coating degradation compared to indoor conditions, particularly for water-based systems, while top coating effectively delays defect formation. Coatings like DSP, BRP, CRP, and DRP maintained structural integrity (0% defect rate), with lower fire resistance rating decay rates of 5.08%～28.79% and controlled bond strength decay after aging. In contrast, ASP, BSP, CSP, and ARP exhibited premature failure (cracking/spalling) due to leakage of expandable components through surface defects. Critically, the degradation of appearance, fire resistance, and bond strength displayed high synchronicity, correlating strongly with changes in content of key elemental and component. Overall, solvent-based coatings outperformed water-based alternatives.

Key words: intumescent fire resistive coatings, outdoor weathering, fire resistance rate, natural aging