ISO 12944 C4 High Corrosion Coating System

Environment Definition

ISO 12944 C4 covers high atmospheric corrosivity. It is often relevant for industrial atmospheres, coastal environments with moderate salt exposure, high-humidity process areas, and structures exposed to more aggressive outdoor service.

Typical examples include coastal buildings, chemical plant steelwork, swimming pool building structures, transport infrastructure, and outdoor industrial equipment.

Coating Selection Logic

C4 projects usually need a multi-layer protective system. The system should be selected around surface preparation, zinc-rich or anti-corrosion primer choice, high-build barrier thickness, and a topcoat that can handle UV, weathering, and the target color life.

For severe marine, chemical, splash, or long-life infrastructure projects, review C5 or CX instead of treating C4 as a universal high-end system.

Starting System Pattern

Layer	Typical role	Notes
Surface preparation	Abrasive blast cleaning is normally expected for new steel	Confirm Sa grade, profile, dust, oil, and soluble salt limits.
Primer	Epoxy zinc-rich, inorganic zinc, or suitable epoxy anti-corrosion primer	Zinc-rich systems need compatible intermediate coats and controlled application.
Intermediate	High-build epoxy MIO or barrier coat	Builds dry film thickness and slows moisture/oxygen penetration.
Topcoat	Aliphatic polyurethane, acrylic polyurethane, fluorocarbon, or project-specific topcoat	Select by UV exposure, color retention, gloss, and maintenance interval.

Technical Review Points

• Confirm whether salt exposure is atmospheric only or includes splash/immersion.
• Review compatibility between zinc-rich primer and intermediate coat.
• Define total DFT and per-layer DFT based on expected durability.
• Confirm current Qilu Paints TDS/SDS, mixing ratio, induction time, pot life, and recoat windows.

Related Qilu Paints Products

• Epoxy Zinc-rich Primer (2K)
• High-build Epoxy MIO Intermediate Coat
• Fluorocarbon Topcoat