What can occur when oil-based coatings are applied over alkaline surfaces?

When oil-based coatings are applied over alkaline surfaces, a chemical reaction known as saponification can occur. This process happens when the alkaline substances present on the surface interact with the oil, leading to the formation of soap-like compounds. Saponification undermines the bond between the coating and the substrate, which can result in a compromised finish that is not durable. The presence of such alkaline substances can occur due to residues of concrete or masonry surfaces or other contaminants that have not been adequately neutralized before coating.

Saponification is particularly relevant when oil-based paints are used because these coatings are more susceptible to the effects of water and alkali, compared to other types of coatings. As a result, the integrity of the coating is jeopardized, which can lead to premature failure of the paint film. In contrast, other potential issues like cracking, peeling, or blistering can stem from different factors such as improper surface preparation, environmental conditions, or application methods, but saponification specifically relates to the interaction between alkali substances and the oil-based coating.