6. Paint surface sinking
The repaired area sinks, and the surface of the topcoat forms a "lake" shape.
① Cause
▶ When spraying multiple layers of paint, the previous layer of paint is not dry enough.
▶ The putty sinks, but it is not easy to be found when spraying low-gloss mid-coat primer, but when spraying high-gloss topcoat, the paint surface sinks.
▶ Multiple layers of wet paint are sprayed in a short period of time, and the interlayer static time of the mid-coat primer and topcoat is not long enough.
② Correction method
▶ All putty layers should be completely dry, especially when the weather is bad or the temperature is low.
▶ Do not apply thick wet paint films of mid-coat primer and topcoat, and the interlayer static time should be controlled as required.
▶ Do not use air blowing to dry the wet paint film surface, because this may cause only the surface to dry, and the solvent inside the paint film cannot be completely volatilized.
▶ When the paint film sinks, grind it to a smooth surface and then re-spray.
7. Pinholes are also called pits, which are dense small holes that appear on the paint film.
① Cause
▶ The compressed air used for spraying contains moisture, or the wrong type or amount of thinner is used in the paint.
▶ Excessively thick wet coating, or forced drying with a hair dryer, or the temperature in the spraying workshop is too high or too low.
② Correction method
▶ The discharge valve of the air compressor that provides the air source should be opened every day to allow the accumulated moisture to flow out.
▶ Avoid excessive thick coating, and ensure the correct solvent evaporation with a medium film thickness. Do not blow dry the wet paint surface, which may cause surface crusting or solvent retention in the film.
▶ Strictly follow the drying rules. Choose the correct thinner and dilute it according to the recommended ratio.
▶ Use the correct spray gun and adjust the pressure to ensure good atomization.
▶ If pinholes occur, sand it until it is flat and repaint.
8. Powdering
The pigment particles in the paint are no longer affected by the adhesive, and the surface of the paint film is powdery, dull, faded and loses its luster.
① Cause
▶ Due to the long-term exposure of the paint film to various climatic conditions such as strong sunlight, the pigment particles in the paint age or loosen, causing the paint surface to gradually peel off in a powdery state.
▶ The wrong thinner is used, which damages the durability of the topcoat layer.
▶ The paint is not mixed evenly.
② Correction method
▶ Choose a suitable thinner and stir the paint evenly before spraying.
▶ Mild powdering can be polished away, and in more serious cases, it is necessary to use coarse wax for polishing. Severe powdering requires re-repairing and spraying.
9. Acid etching
The appearance has rough spots, and the edges of the spots sink into the paint film due to acid etching. Sometimes the color of the paint film changes and the paint surface is uneven.
① Causes
▶ Acidic substances such as asphalt, insect carcasses, and industrial pollutants on the road surface, or grease such as brake fluid spilled on the paint surface during vehicle maintenance, can cause acid corrosion.
▶ Washing before the paint film is dry, or using inappropriate detergents.
▶ The old paint film contains pollutants or polishing agents, and is not thoroughly treated before re-spraying, which can cause acid corrosion of the new paint film.
② Correction method
Immediately remove the above-mentioned pollutants from the paint surface, polish the acid-etched area with coarse wax, and in severe cases, it needs to be polished and re-sprayed.
10. Streaks
Also called streaks or shadows. The surface of the topcoat layer has a difference in color depth, often in a parallel shape, and silver powder paint and pearl paint have the highest probability of appearing.
① Causes
▶ There is too much paint on the edge of the paint fan sprayed by the spray gun, and too little paint in the middle. The possible reasons are excessive compressed air pressure, dirty spray guns, or improper nozzle adjustment. The compressed air pressure should be reduced or the spray fan should be narrowed.
▶ The spraying technique is poor, the distance between the spray gun and the spraying surface often changes or the overlap is uneven during spraying. The distance between the spray gun and the spraying surface should be kept consistent during the spraying process, and a 50% overlap should be maintained.
▶ The paint is not diluted properly, and the thinner is not added according to the process requirements.
② Correction method
If streaks have appeared, wait for the paint surface to dry before spraying a layer of paint again. The compressed air pressure, spray gun adjustment and paint thinner ratio should be correct.
