In the humid and rainy south, water seepage and mold growth on the walls of old houses are a common problem for many families. However, a chemical material called n-octyltrimethoxysilane (CAS No. 3069-40-7) is quietly becoming an "invisible guardian" of building protection. This organosilicon compound, with the molecular formula C₁₁H₂₆O₃Si, forms a dense hydrophobic layer on the surface of substrates such as concrete and stone due to its unique chemical structure. When it comes into contact with the substrate, the trimethoxy group (-OCH₃) hydrolyzes to form silanol groups, which form strong Si-O-Si chemical bonds with the inorganic surface, while the long octyl chains arrange themselves outwards, acting like countless miniature "umbrellas" to block moisture penetration. Technical data from Anhui Aiyota Silicone Oil Co., Ltd. shows that building surfaces treated with this material not only resist rainwater erosion but also effectively resist ultraviolet aging and acid rain corrosion, significantly extending the lifespan of buildings. It is worth noting that this substance has a flash point of 103°C, and application must be carried out in a well-ventilated environment, avoiding open flames. Experts warn that DIY home waterproofing requires caution; professional application is essential to ensure a uniform molecular-level protective layer. As green building standards rise, this environmentally friendly waterproofing agent is gradually replacing traditional asphalt materials, injecting technological power into urban renewal.