Corrosivity categories according to ISO 12944-5

Part 5 of the standard ISO 12944 defines protective coating systems for different corrosive environments: C2, C3, C4, C5-I and C5-M.

Steel surfaces


Corrosivity category C 2 Very low atmospheric-corrosivity category.
Exterior: Atmospheres with low level of pollution. Mostly rural areas.
Interior: Unheated buildings where condensation may occur, e.g. depots, sport halls.


Corrosivity category C 3 Medium atmospheric-corrosivity category.
Exterior: Urban and industrial atmospheres, moderate sulfur dioxide pollution. Coastal areas with low salinity.
Interior: Production rooms with high humidity and some air pollution, e.g. food-processing plants, laundries, breweries, dairies.


Corrosivity category C 4 High atmospheric-corrosivity category.
Exterior: Industrial areas and coastal areas with moderate salinity.
Interior: Chemical plants, swimming pools, coastal ship- and boatyards.


Corrosivity category C5-I Very high (industrial) atmospheric-corrosivity category.
Exterior: Industrial areas with high humidity and aggressive atmosphere.
Interior: Buildings or areas with almost permanent condensation and with high pollution.


Corrosivity category C5-M
Very high (marine) atmospheric-corrosivity category.
Exterior: Coastal and offshore areas with high salinity.
Interior: Buildings or areas with almost permanent condensation and with high pollution.


Im1 Immersion in fresh water.
Im2 Immersion in sea or brackish water.
Im3 Immersion in soil.

Zinc, aluminium and stainless steel surfaces


Corrosivity categories:
C2  Mild atmospheric-corrosivity category
C3 Moderate atmospheric-corrosivity category
C4 High atmospheric-corrosivity category
C5-I Very high industrial corrosivity category
C5-M Very high marine corrosivity category
Im1 Fresh water
Im2 Sea or brackish water
Im3 Soil