Peeling-Poor Galvanized Metal Adhesion
 

Description:
Paint that has lost its adhesion to a galvanized metal substrate.

Possible Cause:
As a rule, paints do not adhere well to smooth metal surfaces. Galvanized metal, a product used to make corrugated sheets, gutters and downspouts, is not only smooth, but the metal is coated with a thin to heavy layer of oil to prevent white rust. When this oily galvanized metal is painted during cold or highly humid conditions, the curing of the paint film is retarded, resulting in wrinkling and loss of adhesion.

Alkyd/oil paints that are applied to galvanized metal will produce acceptable paint adhesion initially, but will quickly fail. The zinc of the galvanize will chemically react with the alkyd binder of the paint, which leads to extreme loss of adhesion.

When galvanized metal is allowed to weather without being painted and is exposed to the atmosphere, the protective zinc coating will oxidize into a white rust until eventually the zinc metal is depleted. The underlying steel will then rust to the offensive red color we are all familiar with.

Solution:
The protective layer of oil must be completely removed. Solvent wiping using a water soluble cleaning agent or VM&P naphtha is recommended for small manageable areas. Most solvents, including mineral spirits, leave a thin layer of residue which leads to adhesion failure of the paint film. This needs to be removed with a detergent solution.

Weathered galvanize develops a layer of “White Rust” which must be removed to ensure good adhesion of the applied paint. Wire brushing is recommended to remove this then wipe clean as listed above.

Iron rust must be removed by wire brushing followed by sanding with an aggressive grit of sandpaper. Severely rusted gutters should be replaced.

Caution: When removing “white rust”, wear a dust mask to avoid inhalation of dust...

Recommended System:
Galvanized (new) Topcoat
2 Coats of Top Quality FLEX BON Exterior Latex Paint
Galvanized (weathered) Topcoat
2 Coats of Top Quality FLEX BON Exterior Latex Paint
Galvanized (rusty) Primer
1 Coat of FLEX BON #190 Series Interior-Exterior Latex Bonding Primer
Topcoat
2 Coats of Top Quality FLEX BON Exterior Latex Paint