Problems with rust-stabilizing coatings
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The main disadvantages of rust-stabilizing coatings include the following: slow rust stabilization speed: These coatings work by using active pigments such as phosphates, chromates, and ferrites to undergo solid-state reactions with rust to form stable complexes; this process is slow at room temperature, and it takes a considerable amount of time to fully stabilize the rust layer. Limited applicability to rust layer thickness: It is only suitable for thin rust layers; generally, the rust thickness should be ≤50 μm, with ≤30 μm being the optimal value ； The effect drops significantly beyond this range. Its corrosion resistance is relatively low: although the resulting complexes can passivate the rust layer, their density and corrosion resistance are inferior to those of traditional anti-rust coatings, resulting in overall poor corrosion protection. Sensitive to the uniformity of the rust layer: If the rust layer is not evenly distributed or if there are areas with thick rust, it may result in incomplete stabilization in those areas, affecting the overall protective effect. Not suitable for high-humidity or water-logged environments: If the paint film does not provide sufficient barrier protection against water vapor and oxygen, residual moisture can cause secondary corrosion.
Indeed, rust-stabilizing coatings have these limitations in practical applications. Regarding the issues raised by the original poster, I would like to add some personal experience: As for the problem of slow rust prevention, it is recommended to extend the curing time of the coating during application; if possible, infrared heating equipment can be used to accelerate this process. We have used a phosphate-based coating from a certain brand in our projects, and its curing time can be reduced by about 30% at 40°C. For dealing with thick rust layers, one can try mechanical rust removal first (using a wire brush or light sandblasting) to reduce the rust thickness to below 50μm, and then use rust-inhibiting coatings. Last year, I worked on a steel structure project, and as a result of those measures, the rust rate showed a 60% reduction during the three-year follow-up inspections. One must indeed be cautious in humid environments. However, we have tested improved formulations with silane coupling agents, and they perform fairly well in environments with a relative humidity of below 80%; yet it is still necessary to refer to the manufacturer’s technical specifications. Such coatings are more suitable as a temporary solution for repair work; for long-term protection, it is recommended to use other coating systems.