ISO 12944 Corrosivity Categories and Coating Systems
ISO 12944 turns “paint the steel” into a specification: where it is, how long it must last, how clean the steel must be, and how thick the coating stack is.
Corrosivity categories
| Category | Environment |
|---|---|
| C1 | Heated indoor, dry |
| C2 | Unheated indoor, rural outdoor |
| C3 | Urban / industrial, humid |
| C4 | Chemical plants, coastal (low salt) |
| C5 | Coastal high-salt, aggressive industrial |
| CX | Offshore, extreme |
Durability class
Low (up to 7 years), Medium (7–15), High (15–25), Very High (> 25). The client’s maintenance strategy sets this; it is the time to first major maintenance, not a warranty.
System selection
Category + durability → a system from the ISO 12944-5 tables: surface prep grade, generic coat types, number of coats, and total nominal DFT.
| Example | System |
|---|---|
| C3, High | Sa 2½; zinc-rich epoxy primer + epoxy MIO + PU topcoat; ~200 µm DFT |
| C5, High | Sa 2½; zinc primer + 2 × epoxy + PU; ~320 µm DFT |
What it means for the estimate
- Surface prep — abrasive blast to Sa 2½ is a major cost and drives grit, containment, and dust control.
- Coat build — more coats and higher DFT means more product (lower m²/L) and more labour passes.
- Inspection — DFT gauging, adhesion tests, and hold points are a QA line item.
EngEst Pro’s Painting Calculator auto-selects a metal coating system from the ISO 12944 corrosivity category you choose, computes total DFT and product volume, and adds surface prep and inspection to the BOM.
Put this on autopilot with EngEst Pro
Create a free EngEst Pro account — 5 projects a month, all 8 calculators, PDF BOQ export. No credit card required.
Create Free Account → Run your first estimate in under 10 minutes.