1.How to assess and pretreat damage?
Determine the scope: The recoating area should include not only the weld itself, but also the heat-affected zones on both sides where the coating has failed due to heat. This typically extends 20-50 mm to each side.
Safety preparation: Ensure the welded area has completely cooled and clean the site.
2.How to perform surface treatment?
Mechanical Treatment (Preferred):
Tools: Use an electric angle grinder with a louvered or fiber abrasive disc.
Objective: Thoroughly remove all weld slag, spatter, scale, and any loose or blistering original coating until a uniform, metallic-luster substrate surface is exposed. For galvanized sheets, minimize damage to the surrounding intact galvanized layer.
Cleaning: Remove all dust and debris generated during grinding with a clean, dry cloth or compressed air.
Chemical Treatment (Supplementary):
If the surface is oily, wipe it clean with a specialized metal cleaner or solvent (such as acetone).
Recommendation: If possible, after grinding and cleaning, spray or brush a coat of phosphating solution or a specialized metal treatment agent onto the exposed steel area to enhance coating adhesion and short-term rust protection.
Final State: The treated surface must be dry, clean, free of grease, free of oxide layer, and have a moderate roughness.
3.How to perform layered coating?
Apply a specialized repair primer:
Purpose: Provides basic corrosion resistance and adhesion.
Material Selection:
Epoxy Zinc-Rich Primer: Optimal choice. Zinc powder provides cathodic protection (similar to the original zinc plating) and offers the strongest corrosion resistance.
Epoxy Primer: Highly versatile, with good adhesion and excellent corrosion resistance.
Two-Component Polyurethane Primer: Good weather resistance and adhesion.
Application: Apply evenly, completely covering the exposed metal area and appropriately covering the surrounding intact edges (approximately 5-10mm) to create a good overlap. Ensure adequate coating thickness.
Applying an intermediate coat (optional but recommended):
Purpose: Increases the overall coating thickness, improving shielding and isolation effects; levels the surface, providing a uniform base for the topcoat.
Materials: Epoxy micaceous iron oxide intermediate coat is a common choice.
Application: Apply after the primer is completely dry.
Topcoat Application:
Purpose: To provide final weather resistance, aesthetics, and chemical resistance.
Material Selection:
Key: Use a topcoat with a chemical system consistent with or compatible with the original color-coated panel's coating whenever possible. For example, if the original panel has a PVDF fluorocarbon coating, a fluorocarbon repair paint is preferred; if it has a polyester coating, a polyester repair paint should be used.
Color Matching: The color needs to be tinted to match the original panel color for optimal aesthetic results.
Application: After the base coat is completely dry, apply 1-2 coats evenly until complete coverage and the desired appearance and thickness are achieved. The coating should extend to the surrounding intact coating for a smooth transition.
4.How to perform curing and inspection?
Curing: Allow the repair coating to fully cure at suitable temperature and humidity. Follow the curing time specified in the repair paint product instructions, and avoid rain, contact with chemicals, or mechanical damage during this period.
Inspection: After curing, inspect the coating for uniformity, absence of missed areas, no runs, and good adhesion.
5.What are the key points to note?
Tools List: Angle grinder, sanding disc (60-120 grit), scraper, wire brush, clean cloth, compressed air, brush or small roller.
Materials List: Special metal cleaner, epoxy zinc-rich primer, topcoat matching the original panel (polyester/silicone-modified polyester/PVDF repair paint), appropriate thinner.
Environmental Requirements: Apply the coating in a dry, low-humidity, well-ventilated environment. Avoid working in rain, snow, strong winds, or direct sunlight.
Safety Protection: Operators must wear masks, goggles, gloves, and other personal protective equipment.