1. Transparent Breathable Sealer (TOP RECOMMENDATION) – Core Coating for Patina Protection
Recommended types: Polyurethane-based weathering steel sealer, silicone-modified acrylic sealer, fluorocarbon transparent sealer (low-VOC grade).
Key properties: High breathability (avoids moisture trapping under the film), water repellency, UV resistance, good adhesion to patina/steel; prevents loose rust and pitting caused by persistent humidity.
Application: 2 thin coats (avoid thick brushing) on stabilized patina (6+ months natural / 1–2 weeks accelerated); reapply every 1–2 years in high humidity.
2. Water-Based Patina Stabilizer – Pre-Coating for Patina Formation
Recommended types: Neutral water-based iron oxide stabilizer (pH 6–8, no acidic components).
Key properties: Promotes the formation of dense, bonded patina, inhibits loose surface rust, and locks in moisture on the steel surface in a controlled way.
Application: Apply 1–2 coats on sandblasted (SA2.5) clean steel before natural patina formation; can be top-coated with transparent sealer for double protection.
3. Epoxy Zinc-Rich Primer (for Critical Structural Components) – Supplementary Anti-Corrosion
Recommended specification: Water-based epoxy zinc-rich primer (zinc content ≥80%), low solvent to avoid moisture trapping.
Key properties: Provides cathodic protection, prevents pitting corrosion on bare steel/ damaged patina; good adhesion to steel substrate.
Application: 1 thin coat on sandblasted steel (for new components) or repaired patina areas; top with transparent polyurethane/silicone sealer within 24h to retain breathability.
4. Coatings to AVOID for SPA-H in High Humidity
Ordinary oil-based paint/epoxy full-coating (non-breathable, traps moisture, causes patina peeling and under-film corrosion).
Acidic rust removers/coatings (corrode SPA-H's alloy elements, destroy patina formation).
Low-adhesion acrylic coatings (easily peel off in high humidity, lose protective effect).
