Painting Systems

Selecting the Right Paint

There are three main steps required to select the right paint to apply over any fabricated, hot dip galvanized structural steel article, once it has been determined the design lends itself to painting in a manner which can achieve uniform paint application. They are:

  1. Identify the environment (Corrosivity Environment – A Quick Guide)
  2. Determine the service life required for the painted structure (see below)
  3. Select the appropriate painting system from the Service Requirement Guide (see below)

If there is any doubt, you should always choose the more aggressive corrosivity environment.

Choosing the service life is often a matter of cost. If the paint system does not last long enough, rectification could be expensive. In the same manner; as the effectiveness of paint systems increase, the materials and application costs rise. AS/NZS 2312 Appendix E provides guidelines on the economics of corrosion protection and the specifier is urged to consider not only the initial cost but also the lifetime cost of any chosen corrosion protection system.

Painting Systems

The following provides guidance on paint systems suitable for use in industrial and commercial situations under six different "service requirements" as follows:

Service Requirement 1 Low corrosivity conditions & medium term service.
Service Requirement 2 Low corrosivity conditions & high resistance to wear & trafficking/long term service.
Service Requirement 3 Medium corrosivity conditions & high resistance to wear & trafficking/long term service.
Service Requirement 4 High corrosivity conditions & high resistance to wear & trafficking/long term service.
Service Requirement 5 Very high corrosivity conditions & high resistance to wear & trafficking/long term service.
Service Requirement 6 Specific industrial chemical or solvent exposure.

Notes

  • Service life: The paint systems listed in this guide provide for either medium or long term service lives, which are typically 5 to 10 years or 10 to 15 years respectively, for a maintenance repainting cycle to retain aesthetic performance.
  • The corrosivity condition assessment is based upon the guidelines of ISO 92239, which essentially relate corrosivity in terms of distance from the seacoast and need careful interpretation. "Corrosivity Environment – A Quick Guide" (page 14) provides assistance on choosing the corrosivity environment.
  • ISO 9223 is preferred over AS/NZS 23128 for reference to corrosivity categories as AS/NZS 2312 is under review at the time of writing and ISO 9223 includes the new extreme corrosivity category CX.

AS 431210 provides excellent guidance for the determination of the general Australian macro    environment with respect to corrosivity zones, but care should be taken when dealing with very high to extreme corrosivity locations (CX) because AS 4312 has not yet been modified to take the extreme zone into account. Otherwise, the corrosivity zones are the same as listed in ISO 9223.

The GAA has no paint system recommendation for category CX at the time of preparation of this guide.

  • Application should be strictly in accordance with the paint manufacturer's written instructions and the relevant recommendations of AS/NZS 2311 in the case of Service Requirement 1 and to AS/NZS 2312 in the case of Service Requirements 2 to 6.
  • For all but Very Low and Low Corrosivity Service Requirements it is recommended that a brush applied stripe coat be applied to corners, welds and other sharp edges to ensure full thickness coverage. Indeed, for High and Very High Corrosivity Conditions it is critical. This is because, unlike galvanizing, paint tends to shrink away from sharp edges.

Service requirement 1

 

Service Requirement 2

 

 

 

Service Requirement 3

 

 

 

Service requirement 4

 

 

 Service requirement 5

 

 

Service Requirement 6

 

Typical Paints

Several paint suppliers are able to offer solutions to the Service Requirements. Unlike Edition 1, the GAA has not offered a listing of suitable paints/suppliers due to regular formula, brand and ownership changes in the paint industry. The GAA recommend direct contact with the paint companies for information on current product availability and suitability. In particular, it is important to establish that the manufacturer provides examples that the particular formulation has been used successfully on galvanized steel.