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There are seven good reasons to paint or powder coat hot-dip galvanized steel:

  1. Extended Durability – in what is called the synergistic effect between galvanized steel and paint, the zinc of the galvanized coating is a barrier protection to the substrate steel, cathodically protects it, and provides underfilm corrosion protection of the paint.  Synergistically, the paint provides a barrier protection to the zinc coating.
  2. Economic – because the zinc extends the life of the paint, less maintenance is required over the entire service life.
  3. Ease of Repainting – when the paint of a duplex system completely weathers, the exposed zinc coating requires minimal surface preparation when repainting.
  4. Aesthetics –  desiring a color to match surrounding structure or for branding.
  5. Safety Marking – the extremely high cost to maintain a very tall structure often means galvanizing is a requirement but those same tall structures are mandated to be painted safety orange and white for high visibility to air traffic.
  6. Extending the Life of Previously Galvanized Steel – large in-place structures often cannot be regalvanized after decades of exposure and so a logical means of keeping the structure in service is to apply a paint, often an inorganic zinc-rich paint which provides barrier protection and some cathodic protection.
  7. Color Coding – steam, water, and other fluid piping systems are often painting in industrial facilities to distinguish them for quick repair and safety concerns.

See Also:
Guide to Preparing Hot-Dip Galvanized Steel for Paint
Duplex Systems

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