What are the common problems of coating process

Sagging
Paint on the vertical surface, and part of the paint will flow under the action of gravity. Make the paint film produce uneven streaks and flow marks. The reason is often that the solvent evaporates slowly and the coating is too thick, such as heavy guns. The spraying distance is too close, the spraying height is improper, the viscosity of the paint is too low, the solvent vapor content in the surrounding air is too high, the airflow is too low, or the geometric shape of the object to be coated is complicated, the paint gathers in the gap, etc. In order to prevent sagging during construction, it is necessary to strictly control the construction viscosity. Improve the proficiency of the operator. Adjust the spray paint distance. One coating should not be too thick.
Bleeding
The color of the primer or substrate is dissolved into the topcoat film, making the topcoat contaminated. The reason is that the organic pigment or resin of the base coat is dissolved by the solvent of the top coat, so that the color penetrates into the top coat. To prevent bleeding, a layer of paint can be used to insulate the primer that has a tendency to penetrate.
Whitish
This means that during the drying process of the volatile paint after construction, the film is dull, muddy or translucent or even whitish. The reason is that the construction site is damp, the atmosphere contains more water, the solvent volatilizes too fast, the surrounding temperature drops sharply, and the water vapor condenses on the membrane, which easily causes the resin or polymer to precipitate and become white. The preventive measures can be organic solvents with high boiling point and slow volatilization speed or preheating the surface of the coated object (to make it about 10°C higher than the ambient temperature). Pay attention to the temperature and humidity of the construction site and the volatilization rate of the solvent.
Bite the bottom
After the top coat is applied, the undercoat layer is bitten up or even separated from the substrate, showing a crepe shape. This is caused by the solvent in the topcoat softening and swelling the primer. The main reason is improper matching of the primer or the primer is not fully dried, or the topcoat is applied too thickly. Attention should be paid to the selection of matching paint, and the top coat should be applied after the primer is completely dry. To prevent biting, the first coat should be thinner, and the second coat should be applied after it dries slightly.