Due to the effect of gravity, the coating may become unevenly distributed during the drying process. On vertical surfaces, it appears like water droplets running down cold glass; on flat surfaces, it looks like downward-flowing streams of hardened liquid. The coating flows downward under gravity, leaving behind a thinner dry film layer.

Cratering occurs when bubbles on the coating surface burst and the coating does not flow back to fill the voids. This creates small holes or depressions on the paint surface similar to volcanic craters. Their size can range from pinholes to diameters of 1 cm (0.40 inches). Larger craters usually appear individually, while smaller craters are often found clustered together in dense groups. Small contaminants can often be seen at the center of the crater.

If the substrate is damp or the coating has poor flow characteristics, voids may form within the coating layer. This defect is mainly caused by contamination mixing into the wet film. Some binders are more likely to form pits when contamination is present. This is believed to be related to changes in surface tension. Pinholes occur before the coating is fully cured. Pitted areas are potential points of coating failure.

Insufficient coating refers to areas where no coating is present, or where the coating has flowed away from the edges of the substrate or weld seams. On rough surfaces, inadequate coating coverage may also expose sharp peaks.

Defect appearance: tiny holes, similar in size to the tip of a sewing needle, scattered across the coating surface. Dust particles or contaminants introduced during the coating process may remain on the paint film surface, resulting in an uneven coating surface with irregular layers and unevenly distributed raised particles.

If the coating is applied too thickly, the internal stress generated during curing may cause cracking.