Can we find a paint for all environments and surfaces?

Different paints can be used to protect a variety of construction materials. No paint can be used in all environments!

Factors influencing the selection of a paint system

• Customer’s expectation (durability)
• Service environment
• Availability of paint and/or other protective materials
• Substrate
• Structure design
• Surface preparation available
• Paint application methods available
• Ease of maintenance
• Cost
• Health, safety and environmental factors

Customer Expectations

• Customers are usually concerned with corrosion and the durability of the asset with aesthetics normally not as important
• To meet their durability requirements coating system durability should be discussed
• According to ISO 12944-1 durability is defined as the expected life of a protective paint system to the first major maintenance painting
• Durability is not the same as a “guarantee” period

Corrosivity of the Environment

• It is important to identify the corrosivity category of an environment since it will relate to:
  • Corrosion rate of the building material
  • Material selection of building products
  • Selection of proper corrosion protection methods for the building materials
• ISO 12944-2 defines the classification of environments by corrosivity category

Corrosivity Categories of Environment – ISO 12944-2 

Description of corrosivity categories

C1 Very low

• Interior: Heated buildings with clean atmospheres, e.g. offices, shops, schools, hotels

C2 Low

• Exterior: Atmospheres with low level of pollution. Mostly rural areas
• Interior: Unheated buildings where condensation may occur, e.g. depots, sports halls

C3 Medium

• 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

C4 High

• Exterior: Industrial areas and coastal areas with moderate salinity
• Interior: Chemical plants, swimming pools, coastal ship- and boatyards

C5- Very high

• Exterior: Industrial areas with high humidity and aggressive atmosphere and coastal areas with high salinity
• Interior: Buildings or areas with almost permanent condensation and with high pollution

CX- Extreme

• Exterior: Offshore areas with high salinity and industrial areas with extreme humidity and aggressive atmosphere and subtropical and tropical atmospheres
• Interior: Industrial areas with extreme humidity and aggressive atmosphere

Im1 Fresh water

• River installations, hydro-electric power plants

Im2 Sea or brackish water

• Immersed structures without cathodic protection (e.g. harbor areas with structures like sluice gates, locks, jetties)

Im3 Soil

• Buried tanks, steel piles, steel pipes

Im4 Sea and brackish water

• Immersed structures with cathodic protection (e.g. offshore structures)

Selecting a paint system according to ISO 12944-5

ISO 12944-5 is an industrial standard which can be referenced to find a suitable system for new construction. There are lists of typical systems categorized by:

• Substrate (low-alloyed carbon steel, hot-dip galvanized steel and thermally sprayed steel)
• Corrosivity category (C1, C2, C3, C4, C5, CX, Im1, Im2, Im3, Im4)
• Expected durability (low, medium and high)

Build-up of a Paint System

There are no “magic” paints that can do everything, hence, multi-layer systems are normal in most cases:

• Primer / Intermediate coat / Topcoat

However, one coat system may also be specified:

• Paint is specially designed for a single coat
• Constant, mild environment
• Minor job such as maintenance
• Low expected durability

Primers are universal for most anticorrosive coating systems and are considered the most important component of the system. The most important properties of primers are listed as follows:

• Adhesion (strong bonding to substrate)
• Cohesion (high internal strength in the film)
• Intercoat adhesion (high bonding to intermediate coat)
• Appropriate flexibility

The principal purposes of an intermediate coat is to provide:

• Thickness for total coating system
• Strong chemical resistance
• Resistance to moisture vapor transfer
• Increase electrical resistance for the coating system
• Strong cohesion
• Strong bonding to primer and topcoat

Topcoats also perform several important functions as they:

• Provide a resistant seal for the coating system
• Form the initial barrier towards the environment
• Provide resistance towards chemicals, water, and weather
• Provide a tough and wear-resistant surface
• Provide a pleasant appearance

Deciding factor is the environment:

An example:

• In a dry inland atmosphere, and indoors 120 µm will be sufficient, while in a coastal environment, 250 - 300 µm may be necessary to achieve the same number of years durability

Number of coats is also of importance

• 100 µm in 2 coats (50 + 50 µm) will give better protection than 100 µm in 1 coat

Where can we find the properties of a paint?

• It is impossible to know all different paint products
• Technical data sheet (TDS) from supplier is a suitable source
• Information that may be found in a TDS or Application Guide:
  • Product description
  • Recommended use and typical paint system
  • Film thickness and spreading rate
  • Approvals
  • Physical properties
  • Surface preparation (methods and requirements)
  • Application (ambient condition, methods, technical parameters)
  • Drying time
  • Brief HSE requirements (Refer SDS)
  • Packing size

Inspectors need to understand and be familiar with the technical data in TDS

Environmental factors not covered in ISO 12944-2

• The Corrosivity categories in ISO 12944 do not cover all situations
• Some factors causing increased corrosion:
  • Heat (high)
  • Chemicals
  • Stray current
  • Mechanical stress
• To find proper paint systems for these environments is not easy
• We can always consult paint supplier and also confirm with pre-qualification testing