Case 1

Introduction

Type of Building: Public building

The surfaces of fresh cement, asbestos cement and plaster are alkaline. Paint usually consist of oils which are really esters, and certain acids and acidic decomposition products. When the alkalies come into contact with the esters and acids, and in the presence of water, saponification will take place.

Newly plastered surfaces are typically highly alkaline. When oil-based paint is applied to these surfaces, such as cement or concrete with a pH exceeding 10, saponification can occur. This chemical reaction produces a soap-like substance when the alkaline surface interacts with the oil-based paint.

Beyond using the wrong type of paint, saponification can worsen due to excessive humidity. Over time, this process can cause the paint to degrade and lose its ability to adhere effectively. It may also result in the formation of unattractive specks on affected areas, diminishing the overall aesthetic appeal of your living space.

Paint saponification occurs when ester bonds within a paint break down due to alkaline conditions and moisture. This type of paint failure causes the paint to weaken and expose the underlying material. The affected paint mixture becomes soft and soluble in water. The process of paint saponification mirrors that of producing soap through saponification. In alkaline environments, high concentrations of hydroxide ions (OH–) attack ester bonds (R-CO2-R’) to form carboxylate ions (R-CO2–) and alcohols (HO-R’). This chemical breakdown breaks down large molecules into smaller, more polar components than esters. These polar components readily interact with water molecules, increasing the paint mixture’s water solubility and reducing its ability to adhere effectively to surfaces. The observed stickiness of the paint during saponification is attributed to these polar molecules, which tend to bond with other polar surfaces.