1 will destroy the phosphating layer and electrophoretic layer, which is very important to prevent the corrosion of metal substrate. After the damage, the ordinary repair process can not be repaired. Therefore, many cars painted with sheet metal are prone to rust, which is the reason.

2. After the metal is repaired by sheet metal, the surface will be uneven. At this time, the surface is usually filled with a filler called putty. This kind of putty has different expansion coefficient from metal, and cracks and depressions will appear after a long time, which will affect the appearance of the surface.

3. In the painting workshop of the automobile factory, the car paint has to be dried at a high temperature of about 200 degrees Celsius. This kind of paint is very hard and has high strength, but the repair shop can only achieve 70~80 degrees Celsius at most, so the hardness and strength of the baked paint are not as good as the original paint.

4. No matter how excellent the painting technology is in the later stage, there will be color difference after a long time, and the repaired paint surface will age faster than the original paint. This is because the repair paint is not as good as the original paint, and the spraying process and environment are also very different from the original paint.

5. After a large area of touch-up, it will have an impact on the preservation rate of vehicles. For example, under the same condition, a painted car is cheaper than a car with slight scratches and no paint.