Painting process appears poor cover, how to solve the bottom?

(1) phenomenon

Due to insufficient coating thickness or poor hiding power of the paint, the phenomenon that the underlying color or pattern can be seen after spraying the topcoat is called poor hiding power, as shown in Figure 9-6. If there are exposed spray parts due to insufficient spraying, it is called exposed bottom or lack of paint.

(2) Reason analysis

The main reason is that the thickness of the paint layer is not enough and the hiding power is poor.

① The paint is not fully stirred evenly before use or the covering power of the paint used is poor. (Related instrument: hiding power paper)

②In order to enhance the gloss of the topcoat, too much varnish is added to the topcoat, resulting in poor hiding power of the topcoat.

③ The construction viscosity (or construction solid content) of the paint is low. (Related instrument: viscometer)

④Use an excessive amount of slow-drying thinner to make the paint form a vertical flow before reaching a sufficient film thickness.

⑤ Spraying is too thin or the number of layers of spraying is too small, or the overlapping degree of spraying width is uneven, and spraying is missed.

⑥ Spraying is not careful or the shape of the object to be coated is complex, and the phenomenon of missing coating occurs-(parts that are difficult to spray, sharp edges, corners).

⑦ The color difference between the primer and the top paint is too large, such as spraying a light-colored paint with high brightness on a dark (especially red) paint surface.

⑧Due to excessive grinding and polishing, the thickness of the paint layer is reduced. (Related Instruments: Thickness Gauge)

(3) Preventive measures

① For parts where the color difference between the primer and the top coat is too large, necessary treatment should be carried out, such as grinding or spraying a layer of gray mid-coat to reduce the color difference between the primer and the top paint.

② Choose a qualified diluent, the paint should be fully stirred, and the construction viscosity of the paint should be properly increased.

③Spray the correct number of layers to achieve the required film thickness. However, the method of spraying multiple coatings to improve the hiding power is not advocated.

④ Improve the proficiency of spraying operation and operate with caution.

⑤ Choose a topcoat with strong hiding power.

⑥ The color and gray scale of the base coat should be as close as possible to the color of the paint. Especially when using pearlescent paint, spray a primer of similar color first, which can save the amount of pearlescent paint and reduce the cost.

⑦Prevent excessive polishing, pay special attention to corner areas.

(4) Remedy

Allow the paint to dry slightly before respraying, or allow it to dry completely, then wet sand and level before respraying.