1. What are the root causes of paint peeling?
Common causes of paint peeling on galvanized color-coated coils include improper surface treatment, incompatible paint, and unfavorable construction environment.
**Incomplete surface treatment:** This is the most common cause. Oil, oxide films, or passivation layers easily remain on the galvanized surface. If not cleaned properly, new paint will have difficulty adhering.
**Incompatible paint:** Galvanized steel is a reactive metal. Using alkyd paints, which release acidic substances, will cause a chemical reaction (forming "zinc soaps"), leading to paint film delamination and peeling.
**Unfavorable construction environment:** Construction in high humidity or low temperature environments will affect the drying and curing of the paint, thus weakening adhesion.
2. How to determine the severity of paint peeling and decide on a repair plan?
A: The repair strategy can be determined based on the area, depth, and presence of rust. Standards such as T/CECS 1162-2022 can be referenced.
Paint Peeling Severity | Judgment Criteria | Recommended Solution
Minor Paint Peeling | Scratches, small localized areas of peeling, no rust | Localized repair
Moderate Paint Peeling | Larger area of peeling, or slight rust | Sanding, cleaning, repainting
Severe Paint Peeling | Large area of coating peeling, severely rusted or perforated substrate | Complete replacement
3. What are the specific steps for repairing galvanized color-coated steel coils?
A: A standard, reliable repair process typically includes the following four steps:
Surface Preparation (the most important step): Thoroughly remove oil, rust, and loose coating from the damaged area. Use power tools or a wire brush to roughen the surface and increase its roughness. Ensure the metallic luster is exposed, then clean it thoroughly with a cloth.
Applying Primer: Select a specialized primer compatible with the galvanized layer (such as epoxy zinc yellow primer, high-zinc cold-dip galvanizing paint, etc.), applying a thin coat to ensure effective coverage.
Applying Topcoat: After the primer dries, apply a topcoat that matches and is compatible with the original coating color. Multiple thin coats are recommended for better adhesion.
Curing and Protection: Allow the sheet to cure naturally at room temperature after application. Before the paint is completely dry, protect it from dust, rain, and other contaminants.
4. Which specialized paint should be chosen for repair?
A: Choosing a paint that is compatible with the galvanized layer and has good weather resistance is key. Below are some commonly used repair paints and their characteristics:
Paint Type | Main Characteristics | Applicable Scenarios
Cold Galvanizing Paint | High zinc content (up to 96%), rust prevention comparable to hot-dip galvanizing, turns a galvanized silver color after drying. | Suitable for repairing missed galvanizing, welding or cutting damage, and scenarios with high corrosion resistance requirements.
Epoxy Zinc Yellow Primer | Specifically designed for stainless steel, aluminum alloys, galvanized parts, etc., with strong adhesion. As a primer, it provides an excellent base for the topcoat.
Specialized Repair Topcoat | Color and gloss highly match the original coating, compatibility tested, single-component and easy to use. | Restores the appearance of small scratches and peeling coatings.
5. What precautions should be taken during the repair process to prevent paint peeling again?
A: The following points should be noted:
Avoid using incompatible paints: Never apply alkyd paint directly to galvanized sheets, otherwise it will easily peel off again in a short period of time.
Ensure surface dryness: Ensure the sheet surface is completely dry and free of moisture before application.
Control repair thickness: If repairing a galvanized layer, the repair thickness should be 50% higher than the original requirement, but generally not exceeding 100μm (approximately 4 mils).
Pay attention to the application environment: It is recommended to apply the paint in a dry, well-ventilated environment. Avoid painting on rainy days or when the humidity is above 85%.