PennCoat, Inc – Adhesion Failure Series – Galvanized Metal

Failure to properly prime galvanized metal typically results in peeling.

When received from a production mill, galvanized metal is very alkaline.  Additionally, the metal is also coated in light oil which protects it from the moisture in the air.  Like most metals, galvanized is no exception to the threat of moisture, and can rust.  The rust will appear white, and will need to be removed by washing with water and a detergent, followed by a thorough rinsing.

Galvanized metal requires specific surface preparation.  The oil coating can prevent proper paint adhesion, and will cause peeling and paint failure.  Additionally, peeling may result if an alkyd or oil-based product is applied over a bare galvanized surface.  Galvanized metal uses zinc, and when the alkyd or oil-based paint reacts with the zinc, it creates a soap film, causing separation and application failure.

Whether you consider industrial painting or home painting, the importance of surface preparation remains the same for galvanized metal. The need for a proper surface preparation is even higher. Metallic surfaces have a lesser tendency for adhesion compared to other surfaces, and if surface preparation is not done properly, paint starts peeling off pretty soon. If you are facing problem of paint chipping off the galvanized metal surfaces, it can be due to any of the following reasons –

  • Improper cleaning of the metal surface – In case, the metal surface is not cleaned, primed or prepared properly before applying paint coating, it will start coming off.
  • Paint coating was applied before applying primer – Primer helps in creating a strong adhesion bond between the coating and galvanized surface. If painting was done before applying primer, it may not adhere properly, and may result in chipping.
  • Paint is applied over newly galvanized metal – If the surface is freshly galvanized, it is very smooth and mostly has a layer of oil over it. The oil prevents white rust. However, that oil is difficult to adhere to, and can cause paint failure and peeling.
  • Painting done in humid conditions – If the application of paint is done in humid or cold conditions, the paint film wrinkles and retards resulting in loss of adhesion of paint.

Galvanized materials are widely used in industries, especially for making doors, gutters, sheets, downspouts, and other components that need to be strong and light weight. Adhesion with the surface is very important for the life of any painted surface and galvanized metal surfaces require special attention due to its chemical make-up and oil coating. Emphasis on proper and detailed surface preparation and help to avoid problems in the future, ultimately increasing the longevity of the product.  When considering industrial or commercial painting, it is beneficial to select a credible painting contractor, like PennCoat, to help avoid the problems that inexperienced contractors may miss.

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