Ensuring the longevity and structural integrity of steel buildings requires a rigorous approach to surface protection. This guide outlines the professional standards for anti-corrosion coating processes, covering everything from surface preparation to final quality inspection.

1. Scope of Application

These standards apply specifically to the anti-corrosion construction processes used in industrial and civil architectural steel structure projects.

2. Construction Preparation

2.1 Material Requirements

• Selection: All materials (primers, topcoats, and thinners) must meet design specifications and national technical standards.

• Primers: Common options include Red Lead oil-based anti-rust paint or Molybdenum-Chromium Red epoxy ester anti-rust paint.

• Topcoats: Options include various colored alkyd enamels and mixed alkyd paints.

• Certification: All products must be accompanied by a manufacturer's quality certificate.

2.2 Essential Equipment

Professional coating requires specialized tools to ensure uniformity and adhesion:

• Surface Prep: Sandblasting guns, air compressors, recovery units, shot blasting machines, and wire brushes.

• Application: Conventional spray guns, professional coating lines (including robotic sprayers), brushes, and rollers.

• Environment: Spray booths and exhaust gas treatment equipment to ensure environmental compliance.

2.3 Operating Conditions

• Personnel: Painters must hold valid special operation certificates.

• Acceptance: The steel structure must pass structural inspection and acceptance before coating begins.

• Safety: The site must feature fire prevention, adequate ventilation, and safety protection to prevent accidents or poisoning.

• Weather: Avoid outdoor construction during high winds, rain, or extreme cold.

3. Operational Process

3.1 Process Flow

Surface Cleaning → Primer Application → Topcoat Application → Inspection & Acceptance

3.2 Surface Cleaning (Pre-treatment)

Surface preparation is the most critical factor in coating durability.

• Sandblasting: Uses compressed air to blast quartz or iron sand. It is the most efficient and thorough method.

• Acid Pickling: Components are submerged in an acid bath. Caution: Must be neutralized with water immediately; residual acid will accelerate corrosion.

• Manual Derusting: Low efficiency and labor-intensive; used only for minor touch-ups.

3.3 Primer Coating

1. Preparation: Mix primers (like Red Lead) thoroughly to ensure uniform viscosity and color.

2. Application: Keep brushing direction consistent. Use the "frequent dipping, short strokes" principle to prevent sagging (runs).

3. Intervals: Allow the first coat to dry completely before applying the second. The second coat should be applied perpendicular to the first to ensure even thickness.

4. Drying: Primers typically require 4–8 hours to reach "surface dry" status before a topcoat can be applied.

3.4 Topcoat Coating

• Site Prep: Clean off welding slag or dust accumulated during transport/assembly. Repair any primer damaged during transit.

• Consistency: Ensure the topcoat color is perfectly matched and stirred well.

• Spraying Parameters: Air pressure should be maintained between 0.4 to 0.7 N/mm².

• Technique: Maintain a distance of roughly 100mm between the nozzle and the surface. Move the gun at a steady speed, keeping it perpendicular to the steel surface.

4. Quality Standards & Inspection

4.1 Mandatory Requirements

• Materials: All coatings and thinners must match design specs (verified via quality certificates).

• Cleanliness: No weld slag, oil, water, or burrs should be present under the paint.

• Integrity: No missing spots, peeling, or "return rusting" (rust bleeding through).

4.2 Appearance Standards

• Qualified: Uniform coating, no obvious wrinkles or bubbles, good adhesion.

• Excellent: Consistent color, no sagging, clear color separation lines, and a smooth, bright finish.

4.3 Thickness Measurement

Use a contact-type film thickness gauge. Take measurements at three points for each spot and calculate the average. Generally, 10% of components (minimum 3 pieces) should be sampled.

5. Protection of Finished Products

• Isolation: Use temporary barriers to prevent foot traffic on freshly painted steel.

• Weather Protection: Cover components if rain or heavy dust is expected within 4 hours of application.

• Transport: Prevent dragging or bumping during shipping to avoid chipping the coating.

6. Common Quality Pitfalls (Environmental Limits)

• Temperature: Best performed between 5°C and 38°C.

• High Heat: Stop operations if the steel temperature exceeds 40℃, as this causes bubbles and reduces adhesion.

• Humidity: Do not paint if humidity is above 85% or if there is visible condensation (dew) on the steel.