There are several reasons why foam occurs in paint.

1. During the production of paint, air will be entrained into the paint due to mechanical stirring.

2. Air brought in during the paint coating process, such as brush coating, roller coating, high-pressure airless spraying, etc.

3. When mixing two-component paint before construction, stir the mixed air.

4. The object to be painted has many pores, and the air that penetrates into the paint is driven out to form air bubbles, such as when painting on porous wood and cement walls.

5. Bubbles generated by chemical reactions, such as polyisocyanate in two-component PU coatings react with trace amounts of water to produce carbon dioxide.