Problems with rust conversion coatings

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Although rust-conversion coatings can simplify the rust removal process and reduce costs, they have several significant drawbacks in terms of application, mainly in the following aspects: high requirements for the condition of the rust layer: they are only suitable for steel surfaces with a rust layer thickness of 40–100 μm and a uniform structure. If the rust layer is too thick, uneven, or if there is residual scale or old coating, the conversion effect will be significantly reduced. Limited options for topcoats: Since paints are usually acidic, they may undermine the stability of subsequent topcoats; therefore, acid-resistant topcoats must be used. It is difficult to control the amount of converter used: if the amount is insufficient, rust cannot be completely converted ； If in excess, the residual acid can cause secondary corrosion, affecting the long-term protective effect. Film-forming properties and corrosion protection level are limited: The corrosion-resistant capacity of the film-forming substance is weak, and the density and corrosion resistance of the resulting coating are inferior to those of traditional primers; therefore, it is usually necessary to apply additional rust-proof primers and topcoats to enhance protection. Sensitive to construction environment: Exposure to humid conditions such as rain or dew before the paint has dried completely can cause the paint film to bubble, become loose, or peel off. Not applicable to all metals: it is primarily designed for iron and steel, and it is not effective on non-ferrous metals such as aluminum and copper. Strict storage and construction requirements apply: some products need to be used immediately after being obtained, as prolonged storage can lead to the formation of precipitates, and high consistency in the operations carried out by the workers is required. In summary, rust-converting coatings are suitable for scenarios with mild to moderate rust and limited conditions, but they are not appropriate for severely corroded areas or critical structures that require an extremely long corrosion resistance lifespan.