ISO 12944 is the international standard for protecting steel structures from corrosion with paint systems. If you have ever seen a specification that says “C4, high durability”, it came from here. Understanding it helps you specify the right system, price work fairly and avoid arguments later.
The nine parts
| Part | What it covers |
|---|---|
| 12944-1 | General introduction, including durability classes |
| 12944-2 | Classification of environments (corrosivity categories) |
| 12944-3 | Design considerations: shapes that are easy to protect and maintain |
| 12944-4 | Types of surface and surface preparation |
| 12944-5 | Protective paint systems |
| 12944-6 | Laboratory performance test methods |
| 12944-7 | Execution and supervision of paint work |
| 12944-8 | Developing specifications for new work and maintenance |
| 12944-9 | Systems and test methods for offshore and related structures |
Corrosivity categories
Part 2 classifies atmospheric environments from C1 (very low) to CX (extreme), based on how quickly unprotected steel and zinc corrode in the first year. Use the picker below for a first indication, then confirm it against the real site: a sheltered corner of a coastal building can behave very differently from the exposed face.
For structures in water or soil there are also immersion categories: Im1 (fresh water), Im2 (sea or brackish water), Im3 (soil) and Im4 (sea or brackish water with cathodic protection).
Durability classes
Durability is the expected time to the first major maintenance, not a guarantee. Since the 2017 revision there are four classes:
- Low (L): up to 7 years
- Medium (M): 7 to 15 years
- High (H): 15 to 25 years
- Very high (VH): more than 25 years
Choosing a durability class that matches the real maintenance plan is one of the simplest ways to save money. Over-specifying adds cost; under-specifying brings the scaffold back sooner.
Using ISO 12944 well
- Agree the environment first. Category and durability drive every other decision.
- Design for coating. Part 3 explains why sharp edges, crevices and inaccessible gaps shorten coating life.
- Specify measurable requirements. Preparation grade, profile, film thickness and inspection points should all be checkable (Part 8).
- Supervise the work. Part 7 covers execution and inspection. The best system on paper fails if it is applied badly.
How we help
We use ISO 12944 every week, from choosing systems for new structures to reviewing specifications that do not quite add up. If you are not sure which category or durability applies, ask us before you commit.
This guide summarises the standard for general understanding. Always work to the current edition and the project specification.