Corrosivity categories and durability ranges

Here you can find explanations for corrosivity categories and durability ranges according to the new ISO 12944-5: 2018 standard.

Atmospheric corrosivity categories and examples of typical environments

C1 - Very Low:

  • Interior refers to heated buildings with clean atmospheres, e.g.  offices, shops, schools, hotels 
  • Not for exterior

C2 – Low:

  • Interior refers to unheated buildings where condensation can occur, e.g. depots, sports halls
  • Exterior refers to atmospheres with low level of pollution: mostly rural areas

C3 - Medium:                     

  • Interior refers to production rooms with high humidity and some air pollution, e.g. food-processing plants, laundires, breweries, dairies
  • Exterior refers to urban and industrial atmospheres, moderate sulfur dioxide pollution; coastal areas with low salinity

C4 - High:

  • Interior refers to chemical plants, swimming pools, coastal ship- and boatyards
  • Exterior refers to industrial areas and coastal areas with moderate salinity

C5 - Very High:

  • Interior refers to buildings or areas with almost permanent condensation and with high pollution
  • Exterior refers to industrial areas with high humidity and aggressive atmosphere

CX - Extreme:

  • Interior refers to offshore areas with high salinity and industrial areas with extreme humidity and aggressive atmosphere and subtropical or tropical atmospheres
  • Exterior refers to industrial areas with extreme humidity and aggressive atmosphere

Categories for structures immersed in water or buried in soil 


  • Fresh water, refers to river installations, hydro-electric power plants


  • Sea or brackish water, refers to immersed structures without cathodic protection (e.g. harbor areas with structures  like sluice gates, locks or jetties)
  • Soil, refers to buried tanks, steel piles, steel pipes


  • Sea or brackish water, refers to immersed structures with cathodic protection (e.g. offshore structures)

Durability ranges

Low - durability until 7 years
Medium - durability between 7 – 15 years
High - durability between 15 – 25 years
Very High - durability over 25 years

Durability is the expected life of a protective paint system to the first major maintenance painting. The durability range is not a guarantee time. Durability is a technical consideration/planning parameter that can help the owner set up a maintenance programme.

NOTE: When the painting system is designed for durability ranges ‘high’ and ‘very high’ in corrosivity categories C4 or higher and in immersion categories Im1 to Im4, the preparation grade must be P3.

Got Interested?