1. Silane/Siloxane-Based Penetrating Sealers (Cost-Effective Alternative)
Core type: Water-based silane/siloxane hybrid penetrating sealers (low solids content, 5–10%)
Key properties: Penetrate 2–5mm into the patina/steel surface (instead of forming a film on the surface), form a hydrophobic silicon-oxygen layer to repel moisture and prevent water absorption, high breathability, and no change to the patina's natural texture/color.
Applicability: Ideal for small SPA-H components (e.g., planters, decorative parts) or as a supplementary protection for sealer-coated surfaces; more affordable than polyurethane/silicone film sealers.
Application: 1–2 coats on dry, clean patina; reapply every 2–3 years (lower durability than film sealers, suitable for moderate high humidity).
2. Acrylic Modified Polyurethane Sealers (Balanced Performance Alternative)
Core type: Water-based acrylic modified polyurethane transparent sealers (weathering steel special grade)
Key properties: Combines acrylic's good adhesion and polyurethane's UV/moisture resistance; moderate breathability, flexible film that resists cracking from steel thermal expansion, and retains the patina's reddish-brown tone.
Applicability: A middle option between pure acrylic and pure polyurethane sealers; suitable for SPA-H structural parts (e.g., steel frames, sculpture bases) in high humidity with moderate anti-corrosion requirements.
Application: 2 thin coats on stabilized patina; reapply every 1.5–2 years (better durability than silane sealers, lower cost than pure fluorocarbon sealers).
3. Polyurea Thin Coatings (Heavy-Duty Moisture Resistance Alternative)
Core type: Spray-applied aliphatic polyurea transparent thin coatings (thickness 50–100μm, avoid thick coating)
Key properties: Ultra-high water resistance and chemical resistance, fast curing (cures in seconds), flexible film that adheres tightly to patina, and resists persistent moisture immersion in extreme high humidity (e.g., tropical rainy areas).
Applicability: For critical SPA-H load-bearing components in extreme high humidity (e.g., outdoor bridge guardrails, coastal high-humidity zone structures) where standard sealers lack sufficient moisture resistance.
Application: Must be spray-applied on dry, dust-free patina; top with a small amount of UV stabilizer if needed; reapply every 3–4 years (higher durability, slightly higher construction cost).
4. Wax-Based Patina Protective Coatings (On-Site Quick Repair Alternative)
Core type: Microcrystalline wax/paraffin-based water-dispersible protective coatings (weathering steel special)
Key properties: Forms a thin, hydrophobic wax film on the patina surface, repels surface condensate and light moisture, easy to apply (brush/spray), and can be removed if needed (suitable for temporary protection).
Applicability: For on-site quick repair of small damaged patina areas (e.g., scratches, chipping) in high humidity, or temporary protection for SPA-H components during transportation/installation.
Application: 1 thin coat on clean patina damage; reapply every 6–12 months (temporary protection, not for long-term structural use).
Critical Notes on Alternative Coatings
All alternatives cannot replace the foundational pre-treatment (SA2.5 sandblasting + degreasing + drying) of SPA-H; a clean, dry surface is required for all coating adhesion.
Avoid mixing different coating types (e.g., silane sealer + polyurea coating) on the same surface, as this causes poor adhesion and film peeling.
For extreme high humidity (humidity >90% for long-term), pair alternative coatings with structural optimization (drainage/ventilation) for double protection-coatings alone cannot offset moisture trapping from poor design.
