Understanding degradation mechanism for long-term natural weathering of building silicone sealant to guide future façade design, inspection, and accelerated testing methods

• Comprehensive characterization of 36-year old silicone sealant from a high-rise tower was conducted. • Severe weathering degradation, such as erosion and cracking, was demonstrated. • Key degradation mechanisms were analysed by advanced microscopy and spectroscopy. • Acid rain emerged as a key factor, exacerbating the observed deterioration. • New insights into the natural weathering of silicone materials is provided. Silicone sealants play a central role in the structural integrity and sealing performance of modern building façades. Yet, due to its relatively recent implementation in construction, little is known about its long-term degradation behavior in building contexts. Herein, we analyzed the degradation mechanisms of silicone sealants exposed to more than three decades of natural weathering in a high-rise tower façade. Our findings revealed that acid rain is the most detrimental factor to the silicone material – leading to the dissolution of the filler particles and inducing hole defects and microscale cracking. At a slower rate, the weathering exposure also led to the deterioration of the silicon-carbon atomic structure. The observed degradation led to a marked decrease in elongation capacity and an increase in the modulus of elasticity of the material. Nonetheless, the visual appearance and mechanical properties of the weathered sample still conformed with performance standards – reiterating the excellent durability of silicone in building assets. Overall, the obtained knowledge serves as a reference for future weathering studies on silicone and similar elastomeric materials as well as guide future façade design and inspection guidelines.