The paint applied on the vertical surface flows downward, causing uneven streaks and flow marks in the paint film. According to the shape of the flow marks, it can be divided into sinking, sagging, and flowing.

Subsidence: 

local vertical flow between the coatings during the period from the completion of the coating to the drying, resulting in semi-circular, ice tumor-like, and wavy phenomena with uneven thickness.

Sagging: 

In the case of dipping, showering, spraying, brushing and other coating methods, after the coating accumulates on the vertical surface and the edge of the object to be coated, it is fixed and firmly attached as it is.

Sagging: 

The phenomenon of sagging in a large area of the paint film on the vertical surface of the object to be coated.

Reason:

(1) The solvent used evaporates too slowly or does not match the paint.

(2) One-time coating is too thick, improper spraying operation, too many heavy guns, or incorrect spraying distance and angle.

(3) The viscosity of the coating is low.

(4) The ambient temperature is too low or the solvent vapor content of the surrounding air is too high.

(5) When new paint is applied on a smooth paint film, it is also easy to produce sag.

Prevention:

(1) Select the solvent correctly, pay attention to the solubility and volatilization speed of the solvent.

(2) Improve the proficiency of spraying operation, spray evenly, pay attention to the correct distance and angle of the gun, and do not apply too thick at one time (generally controlled at about 20 microns). If a paint film after spraying (30-40) microns at one time is required, new technologies and new Material.

(3) Strictly control the construction viscosity and temperature of the coating.

(4) Strengthen the ventilation, and keep the ambient temperature of the construction site above 15℃.

(5) The new paint on the old paint film should be sanded in advance.