Peeling From Galvanized Metal: By Vancouver’s Best Painters

Galvanized metal is very alkaline when received from the mill. In most cases, it also has an oil on its surface that prevents atmospheric humidity from coming in contact with the surface. This oil normally disappears naturally during the first six months of weathering; however, it must be removed if the customer wishes to paint before then. The oil is removed by solvent wiping or detergent washing. The alkalinity is then neutralized by acid wiping the surface with phosphoric acid followed by fresh water rinsing.

Failure to properly prime galvanized metal is usually the cause of peeling. When galvanized metal is allowed to weather for six months, it will develop white rust. This is the appearance of a white haze which dulls the galvanizing after exposure to the elements. This white rust must be removed by washing with water and detergent, followed by a complete rinsing.

Galvanized metal is usually specially treated to remove chemicals deposited on the surface after the galvanizing bath. Otherwise, peeling may occur (Figure 7). Peeling may also occur when an alkyd or oil-based product is applied over a bare galvanized surface. A chemical reaction occurs between the zinc metal used in the galvanizing process and the alkyd resins in the coating. When this reaction (called saponification) occurs, a soap film forms between the galvanized metal and the alkyd or oil coating.

Rusting also can cause peeling. Check the backs of the paint chips for signs of rust. Rusting often occurs because of failure to paint immediately after cleaning the metal surface.

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