1. Feasibility Analysis of Local Patina Removal
The local patina is loose, uneven, or has pitting corrosion due to long-term accumulation of moisture, dirt, or contact with corrosive media.
The local surface is damaged during processing or installation, leading to the formation of rust with poor protective performance.
The project has strict requirements for the uniform appearance of the steel plate, and local discoloration of the patina needs to be adjusted.
2. Standard Process for Local Patina Removal & Paint Touch-Up
Step 1: Local Patina Removal
Mechanical removal method (recommended): Use a fine abrasive tool (e.g., 200–400 mesh sandpaper, a soft wire brush, or a low-pressure sandblasting machine with fine sand) to gently polish the local patina until the fresh, uniform steel substrate is exposed. Avoid excessive grinding that causes deep scratches on the surface.
Chemical removal method (for small areas): Use a dedicated weathering steel rust remover (weak acidic formula, pH 3–5) to wipe the local area. After the patina is softened, rinse it with clean water and dry it immediately to prevent residual acid from corroding the steel substrate. Do not use strong acids (e.g., hydrochloric acid, sulfuric acid) to avoid damaging the alloy element distribution on the surface.
Step 2: Surface Pretreatment Before Touch-Up
After removing the patina, clean the surface with anhydrous ethanol or a dedicated degreasing agent to remove dust, oil stains, and residual rust remover.
Ensure the surface is completely dry (moisture content ≤5%) to prevent the paint film from blistering or peeling due to trapped moisture.
Step 3: Selection of Touch-Up Paint & Application
Paint type selection (core requirement): Must use weathering steel-specific breathable protective paint (e.g., acrylic weathering steel paint, fluorocarbon paint for rusted steel). Do not use non-breathable paints (e.g., epoxy resin paint, alkyd paint), as they will block the contact between the steel surface and air/moisture, preventing the reformation of the natural patina and causing hidden corrosion risks under the paint film.
Application process:
Stir the touch-up paint thoroughly to ensure uniform pigment dispersion.
Apply the paint in thin layers with a small brush (avoid thick coating), with a single coat thickness of 20–30 μm.
After the first coat is completely dry (drying time depends on the paint type, usually 2–4 hours at room temperature), apply a second coat if necessary to ensure full coverage of the repaired area.
Allow the paint film to cure naturally for 7–10 days to form a stable protective layer that is compatible with the surrounding natural patina.
3. Key Precautions
Avoid large-area patina removal: Only remove and touch up the problematic local area. Large-area removal of the intact patina will destroy the overall protective system of the steel plate and increase the risk of uniform corrosion.
Paint color matching: Select a touch-up paint color that is consistent with the surrounding natural patina (usually reddish-brown or dark brown) to maintain aesthetic consistency.
Post-maintenance: After touch-up, regularly inspect the repaired area. If the paint film is found to be peeling or cracking, reprocess it in a timely manner. In outdoor environments, the touch-up paint film can maintain stable performance for 3–5 years, after which it needs to be re-coated.
