The correct repair method of car paint scratches

Inadvertently there will be scratches on the paint surface of your car. Don't remember that the car will scratch with other cars during driving, or scratch with roadside branches, or in storms, dusty weather and “flying sand and stone”. Scratches occur, so how can there be scratches on the paint surface of the car? Perhaps it is due to scratches caused by the following two reasons:

1. Improper scrubbing. When the car is scrubbed, if there are hard particles in the cleaning agent, water or scrubbing tools (sponges, towels, etc.), the paint will be scratched.

2, improper care. When polishing the paint surface, if the selected grinding disc has a large particle size, the grinding force is heavier or the grinding is missed, it will leave different degrees of scratches on the paint surface. Also, when waxing, if you choose the wrong type of wax, if you mistakenly use sand wax on a new car, you will get a circle of scratches.

So when the paint surface of the car is scratched, how do you deal with it? We can make different treatments according to the depth of scratches on the paint surface of the car.

Treatment of shallow scratches

Shallow scratches are slight scratches on the surface paint. The scratches have penetrated the varnish layer and have damaged the colored paint layer, but the colored paint layer has not been scratched through. For the car body with slight scratches on the surface paint, the surface paint has not been scratched through the inspection. The following repair process can be used for repair.


First, remove the glazing wax film layer, oil film and other foreign matter on the surface of the paint. The method is to clean the scratched part with a dewaxing cleaning agent, and then dry it.


According to the size and depth of the scratch, select appropriate sanding materials, such as 1500 grindstone, 9um grinding disc or cosmetic mud to sand the scratched surface layer. Grinding is generally performed manually, and it can also be polished with a grinding/polishing machine or a grinder. Be careful not to wear through the paint surface layer when hitting. If the paint surface layer is worn through and the middle paint layer is revealed, the paint surface must be sprayed to remedy it.


The polished lacquer surface has been basically cleared of shallow scratches, and some hairline scratches, spin printing, etc. remaining in the polishing operation can be treated by the lacquer surface reduction. The method is: use a small piece of non-woven fabric to evenly smear the reducing agent on the paint surface, and then polish until the paint surface layer is completely consistent with the original coating color.


The waxing treatment should be carried out after the lacquer surface is restored. The method is: first mash the solid polishing wax, put it in gasoline and heat it for later use. Use clean cotton yarn to moisten the repaired part with gasoline, then dipped in wax and wipe it all over. Wipe repeatedly until the paint is smooth. Until the light is bright. When waxing, the entire surface of the car can also be waxed and polished at the same time. The method is: wipe off all the wax with clean cotton yarn, and then apply light wax until the lacquer is clear and shiny. *After that, wipe it all with a flannel.

Quality inspection

After the above procedures are completed, the appearance quality of the repaired surface should be inspected. The focus of the inspection is that the color of the coating must be exactly the same as the original paint surface. If there is a difference, it means that the surface cleaning and waxing and polishing are not completely in accordance with the requirements. Rework.

Treatment of moderate scratches

Moderate scratches mean that the colored paint layer has been scratched, but the primer layer has not been damaged; deep scratches indicate that the primer layer has been scratched, and when the colored paint layer has been scratched, but the underlying paint has not been damaged, it is repaired the way is:


Check whether the bottom paint is well attached; polish the scratched parts of the middle coat and top coat to make them flat and smooth; trim the edges of the damaged parts so that no scratched coating is visible on the edges, if necessary The polishing area can be appropriately expanded.

Washing and drying

Use a special cleaning agent to remove oil, wax and other foreign matter on the polished surface; use drying equipment to dry the cleaned surface.

Medium coating coating

1. Determine the construction process parameters, and determine the construction viscosity, atomization pressure, coating distance, drying temperature, drying time and other parameters according to different coatings;

2, cover, cover the parts that are not sprayed.

3. The middle coat paint is dried. If the repaired area is not large, it can be dried naturally at room temperature, but the time is longer; generally, far-infrared drying lamps or far-infrared drying ovens (reflective) are commonly used for partial drying.

4. Polish and clean the middle coat paint surface. After the middle coat paint surface is dry, lightly sand the repainted paint surface with No. 320 sandpaper to make it smooth and flat, and there is no rough feeling when touched by hand. There are two kinds of sanding methods: dry sanding and wet sanding. When dry sanding, use compressed air to clean the sanding parts, and then use a clean sticky rag to wipe off the floating dust. When wet sanding, use 320# water sandpaper to polish the surface of the repaired middle coating. Hand touch until there is no roughness, and rinse with water, wipe the water, dry or blow dry with compressed air, best use far-infrared light box to dry.

Lacquer painting

1, ** paint finish.

①Spray paint: According to the requirements of the construction conditions, adjust the selected paint surface to the allowable range of the specified process conditions, and then spray.

②Drying: Generally, special far-infrared baking lamps or ovens are used for partial drying. The baking temperature and time depend on the actual conditions on site, but must meet the baking quality requirements. The cotton ball method can be used to determine whether the paint film surface is actually dry.

③Grinding: Use 320# sandpaper to polish the paint surface to make the surface of the paint finish smooth, and wipe it with a rag and compressed air while blowing, and then wipe the surface thoroughly with a sticky rag.

2, the second top coat.

①Spray painting and drying are the same as the first time.

②Grinding: The finish polishing is a post-grinding process that directly affects the surface quality of the coating. Special attention should be paid to the quality of the polishing. Use 500-600 grit sandpaper to lightly wet and sand to eliminate coating film defects, and then dry it.

varnish coating

After the second top coat is sprayed, polished and dried, another layer of amino varnish should be sprayed.

1. Construction conditions: Take overcoat KH-24 as an example, use special thinner KH-24; dilution rate 14%-16%; dilute viscosity 24-25s; construction solid content 46%; stability and standing for 48h .

2, coating method: spraying times 5-6 times, the target thickness is 35-40um. Leveling between each time is 3-5min; *the last leveling time is 7-10min.

3. Drying: drying temperature is 140°C, drying time is 30min. If the holding drying time is 20min in the drying room. If it is a small area of ​​local drying, use far-infrared heater for baking, and the time is based on the actual drying time.

polished and waxed

The operation method of polishing and waxing is: first soak the polishing agent with cotton cloth, woolen cloth, sponge, etc., perform polishing, and then wipe it off. Then apply light wax and polish it.

Treatment of deep scratches

Deep scratches include scratches, which are local damage to the car body, plate surface deformation, cracking and other traumas caused by collisions, scratches, etc., and serious damage to the coating.

For deep scratches, the old paint layer that damages the board surface should be removed first, and the damaged board surface of the car body should be repaired by means of sheet metal or welding, so as to meet the requirements of the original shape, size and contour. Then repair painting, the process method is:

Surface treatment

Use a spatula, wire brush, etc. to remove the surface coating, rust, and welding slag. The large weld is smoothed with a grinding wheel, and polished with 1.5-2.5 emery cloth to remove rust and debris on the bottom surface; use a solvent to remove the scratches Clean and dry; apply a thin layer of primer; apply a layer of anti-rust paint on the surface of the primer.

Scratch putty

Cover the quick-drying putty on the metal layer; after the putty is dried, use 400# dry sandpaper to smooth the putty; wipe off the scratches with a dewaxing cleaner.

Spraying middle coating

Cover the unpainted area with special adhesive tape; first use a spray gun to lightly spray two primers, and then spray the second thicker primer, and let it dry; use 600 grit sandpaper to smooth the primer ; If the scratches are still lower than the paint surface, you can spray 3-5 layers of primer and repeat the cleaning steps; use 1500-2000 sandpaper to smooth the surrounding parts, and then wipe with a solvent.

spray top coat

1. Spray paint: select the top coat matched with the original car color paint, mix it according to the original car color, and adjust it to a viscosity that meets the construction requirements, and then spray it after filtering. After each spraying, there should be the leveling time required for the coating film, and then spraying over and over again. Make the first top coat coating reach 30um-40um thickness. The coating should have enough time for leveling and drying after coating, and it is generally more than 2h to dry at room temperature.

2. Warm grinding: Use 280-320 water sanding paper to polish the coating film on the basis of spraying four layers of coating film smoothly. Use a rag or compressed air to wipe clean while blowing. And make the surface dry, it can be heated to dry, or it can be air-dried naturally. However, it takes a longer time to dry naturally, so care should be taken to prevent dust from contaminating the surface of the coating film.

3. Finishing: In the original topcoat, add less than 20% of the varnish, and then appropriately add a thinner to mix and use to increase the smoothness. Its viscosity is preferably 15s/25Oc. Spray after filtering. After spraying, the leveling property should be good, so that it is easy to polish and wax the next day. The total thickness is 80-110um.

polished and waxed

The editor recommends using tortoise scratch wax to treat micro scratches. Once thrown, it will be bright, delicate, uniform, safe, and instantly regain the feeling of a new car.

The automotive parts and parts machining, PTJ Shop offers the highest degree of OEM service with a basis of 10+ years experience serving the automotive industry. Our automotive precision shop and experts deliver confidence. We have perfected the art of producing large component volumes with complete JIT reliability, backed by the quality and long-term reliability our customers expect.

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