What Does Flaking Mean?
Flaking refers to a paint failure, where the paint lifts up and peels away from the substrate due to the loss of adhesion. When paint is applied over a moist, greasy, chalky or any other improper surface, flaking is the most likely result. Flaking causes paint failures, which lead to corrosion of the substrate such as rust. The causes of flaking can be:
- Poor-quality paints that possess poor adhesion and flexibility
- Improper surface preparation
- Thin layer of paint coating
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Corrosionpedia Explains Flaking
Flaking is a condition of paint failure where tiny pieces of coating lift up from the surface of the substrate. Flaking is commonly seen on wooden surfaces, e.g. on fences and old wooden buildings. It can also occur on metal surfaces especially galvanized surfaces. Flaking can be prevented by cleaning surfaces properly and by using a coating that possesses strong adhesion and good aging characteristics.
When alkyds or oil-type paints are applied on galvanized surfaces and age, they oxidize to the point where the paint film shrinks and pulls itself away from the surface. Here, an interfacial chemical reaction also occurs, which creates a zinc soap between the organic coating and the zinc substrate. This ultimately causes adhesion loss of the coating substrate, as well as flaking.
Flaking usually begin with thin, hairline cracks in the paint film, which grow with time. Flaking is caused by decomposing paint and is different from efflorescence or mottling, which display white, crusty mineral salt deposits that have leached from mortar, concrete or masonry surfaces behind the paint. Rust usually appears as orange flaking on a surface.