1. Optimize surface pretreatment before conversion
Thoroughly remove loose rust, dust, oil, grease, and welding slagLoose contaminants prevent the conversion agent from bonding tightly to the substrate.
Use hand grinding, wire brushing, or light sandblasting to keep only tight, stable rust layers.
Do not use strong acid pickling, which over-corrodes the surface and weakens adhesion.
2. Select high-quality rust conversion agents
Choose formulations based on phosphoric acid, tannins, or organic chelatorsThese form stable iron phosphate or organometallic complex layers.
Avoid low-cost products with high acidity, which cause brittleness and easy cracking.
Prefer agents with added corrosion inhibitors and adhesion promoters for longer durability.
3. Strictly control construction environment and conditions
Apply only when temperature is 10–35°C and relative humidity < 85%High humidity or low temperature leads to incomplete reaction and poor film formation.
Ensure sufficient drying time (usually 6–24 hours) before topcoating.
Avoid application in rainy, foggy, or dusty environments.
4. Apply a matching intermediate or topcoat system
After rust conversion, apply epoxy primer + polyurethane topcoatThis seals the conversion layer and blocks moisture, oxygen, and UV damage.
Use transparent weather-resistant topcoat if you want to keep the rust-color appearance.
Never leave the conversion layer uncoated - it will gradually powder and peel without protection.
5. Ensure uniform film thickness and coverage
Too thin → insufficient protection; too thick → easy to crack and peel.
Recommended dry film thickness: 15–30 μm for conversion layer.
Avoid missing corners, welds, and edges, which are prone to early failure.
6. Improve structural design to reduce harsh exposure
Avoid long-term water immersion, dirt accumulation, and crevice corrosion
Improve drainage and ventilation to reduce humidity contact.
Isolate Q355NH from materials that trap moisture (wood, soil, concrete).
7. Perform regular maintenance and touch-up
Inspect the coating every 1–2 years for blistering, cracking, or rust penetration.
Clean the surface and touch up damaged areas in time to prevent expansion.
Renew the topcoat every 3–5 years in severe outdoor environments.
8. Avoid damaging the conversion layer during fabrication
Minimize bending, collision, and scratch after coating.
Repair any damaged areas immediately before exposure.
