Due to the many processes in the painting operation, the probability of paint surface problems is still very high, usually due to improper treatment of the putty layer or primer layer, lack of control of the painting process, poor working environment, and paint composition deviation.

If you find a problem during the painting process, you can stop the operation and take appropriate measures immediately. Depending on the problem, you can also wait for the painting process to finish before dealing with it.

Let's analyze the common paint defects and treatment methods in spray painting operations. The following is the text:

[1] Shrinkage

Wrinkling or shrinkage of the topcoat surface during the painting process or while the film is drying is most common in alkyd paint repair jobs.

(1) Cause

① Improper drying method leads to uneven drying of the paint surface. If the freshly sprayed paint layer is dried or forced dry too quickly, or if the paint shop temperature is too high, the paint on the surface dries faster and shrinks, which will delay the drying of the inner paint. When the inner layer of paint dries, the surface paint will shrink. Avoid painting in workshops with inappropriate temperatures or in workshops with large temperature changes.

② If the paint layer is too thick or too wet, the inner layer of paint will not be able to release the solvent and dry at the same speed as the outer layer of paint, and the paint surface will be deformed and wrinkled. Multiple sprays should be used to reduce the thickness of the one-shot topcoat.

③ The wrong diluent or incompatible material is used. Shrinking can be caused by using fast drying thinners or using volatile paint thinners in enamels. The fast-drying diluent must be used in accordance with regulations, and the amount of fast-drying diluent should be reduced in high temperature seasons.

(2) Correction method: After the paint is fully dried, remove the shrinking paint surface and repaint it.

[2] uplift

Also known as wrinkling. During the painting process or the drying process of the paint film, the bulge formed in some areas due to the expansion of the paint surface may take on a different shape.

(1) Cause

①The wrong thinner is used. The use of volatile paint thinners in enamels promotes the bulge of the interior paint layer, which ultimately results in the bulge of the topcoat layer.

②Incompatible raw materials are used. The newly sprayed paint layer has chemically reacted with the original paint layer, or the defects of the original paint layer have not been properly handled, and the paint layers are separated from each other, causing the top paint layer to bulge.

③ The bottom layer is not thoroughly cleaned, for example, the grease or wax on the surface of the bottom layer is not completely removed, and the re-sprayed paint cannot be attached due to the influence of the interlayer effect.

④ The interval between secondary spraying is too short, and the primer paint is not given sufficient drying time, which causes the solvent in the wet paint surface to erode the primer or topcoat to soften it.

(2) Correction method: Polish the defective area until it is smooth but cannot be worn through, and repaint it.

[3] Sag

Also known as weeping or weeping. The coating is locally thickened, and a vertical flow state occurs due to gravity, which only occurs when the sprayed surface is placed vertically or the surface that is sprayed vertically.

(1) Cause

① The thinner was used incorrectly. Usually a slow drying diluent is used or an excess of diluent is used.

② Improper use of the spray gun. For example, the compressed air pressure is too low, or the distance between the spray gun and the spray surface is too close, or the speed of the spray gun is too slow, which will increase the possibility of sagging. The jet shape and jet air pressure should be properly adjusted to keep the jet distance at 20-25cm, and the moving speed of the spray gun should be uniform. Grasp the limit spray amount that will cause sag, and focus on spraying while observing the film formation.

③ The temperature of the spraying workshop is too low, the sprayed paint layer is not easy to dry, or the one-time sprayed paint layer is too thick, resulting in a slow drying speed of the paint layer.

④ When spraying the subsequent paint layer, allow enough drying time for the previous paint layer. Allow enough time for the paint to rest and level before placing the sprayed surface vertically.

(2) Correction method: When the sagging phenomenon is slight, after the paint surface is dry, wet sand the defective area with fine sandpaper, and then wax and polish. When sagging is severe, sand the defective area and repaint.

[4] Wet printing or wax marks under the coating

From the surface of the paint layer, you can see the outline of the contaminated area on the bottom layer, or the appearance of matt spots of various shapes.

(1) Cause

① The underlying surface is not thoroughly cleaned before painting, for example, grease or wax is not completely removed.

②The previous paint layer has not dried or the defects of the old paint layer have not been removed.

③ The previous paint layer is incompatible with the paint layer sprayed again.

(2) Correction method: If the wet print is obvious, the paint layer should be polished off and then sprayed again.

[5] Watermark

White or yellow corrosion-like spots appear on the surface of the paint.

(1) Cause

①The paint layer has come into contact with water droplets, especially water with high mineral content, without adequate drying. When the water droplets mix with the solvent in the paint, they can penetrate the paint surface, leaving a trail of water. Therefore, the paint surface after spraying is strictly prohibited to contact with water, and it is strictly prohibited to drive in rainy days.

② Even the dry paint surface will leave water marks on the paint surface if it is frequently exposed to water droplets. Under sunlight, the water droplets have the transmission focusing function of a magnifying glass, and after the water droplets dry, they leave a white or yellow corrosion outline on the paint surface.

③ If the sprayed paint surface is too thick, the drying time will be prolonged, and the probability of leaving water marks after the paint surface contacts with water droplets is greater.

④Silicon-containing polishing materials are used prematurely on the paint surface that has been sprayed soon.

(2) Correction method:

If thick waxy paint is suspected, the paint should be thoroughly cleaned with a solvent before polishing. Polish with a finer polish or a coarser polish, depending on how deep the watermark is. In the case of particularly serious watermarks, the watermarks will reappear after a few days of polishing, and the cleaning and polishing procedures should be repeated several times to completely eliminate the watermarks. If repeated polishing does not work, wet sand the watermarked area with fine-grit sandpaper and repaint.

[6] Wire walking

That is, the reflection of silver powder is uneven. The silver powder particles are arranged in the same direction, showing light and dark stripes. In most cases, the deposited silver powder will puncture the paint film if wire run-off occurs on vertical surfaces.

(1) Cause

①Silver powder paint is a mixture of pigments, solvents, metal particles with a certain size and additives. The distribution ratio of metal particles in the pigment will affect the color of the paint surface. If the silver powder paint is not fully stirred before spraying, metal particles will be deposited on the bottom of the container, resulting in too many metal particles in the paint at the bottom, making the paint film too thick and uneven paint color.

②The viscosity of the paint is incorrect, that is, the ratio of the thinner is wrong. If the amount of thinner is too much, the drying speed of the paint surface is very slow, and the metal particles are easy to aggregate, which is prone to the phenomenon of wire running. However, if the amount of thinner is too small, the quality of the paint film will be poor, and an appropriate viscosity that can take into account both requirements must be selected.

③ The time interval of each spraying is too short. If the silver powder paint is not fully dried, uneven distribution of metal particles will occur.

④ Improper adjustment of the spray gun or poor painting technique. If the compressed air pressure is too low, or the distance between the spray gun and the sprayed surface is too close, or the speed of the spray gun is not uniform, it will cause the phenomenon of light and dark on the surface of the silver powder paint.

(2) Correction method:

Re-spray the paint surface after water grinding with fine sandpaper, or increase the compressed air pressure after the paint surface is completely dry, increase the distance from the spray gun to the sprayed surface to 40-50cm, and then spray a layer of silver powder paint with quick-drying thinner.

[7] Fisheye

Also called shrinkage or beading. Circular pits appear on the topcoat, sometimes scattered and sometimes aggregated.

(1) Cause

① Silicone-containing wax is the most common cause of fish eyes. Abrasives on sandpaper, as well as many car waxes and polishes, contain silicone, which has a strong adhesion to paint and can be difficult to remove. Very small amounts of car wax can cause fish eyes, so make sure all work with silicone is done in a segregated workshop away from the paint shop.

②The surface of the primer is contaminated, for example, there is oil on the primer, so the sprayed surface must be cleaned before spraying, and a neutral detergent can be used.

③ Strictly filter the compressed air used by the spray gun to ensure the purity of the compressed air, because silicones are often found in compressed air pipes rather than paint. Drain and clean the compressed air filter daily to remove moisture and dirt from the filter, and drain the air compressor daily.

④ It is not recommended to use paints containing anti-fish-eye remover, because the remover may contaminate other surrounding sprayed parts, and in severe cases, it can lead to a decrease in the adhesion of the topcoat.

(2) Correction method: remove the affected area and repaint.

[8] poor covering power

Also known as translucent or bleed. The color paint cannot completely cover the color of the original paint surface, or the color of the old paint film and the color of the primer layer penetrate into the top paint layer, changing the color of the top paint. The red and yellow paint layers show more bleeding.

(1) Cause

①Precipitation occurs in the paint. After the topcoat is diluted, without adequate stirring, the pigment is deposited on the bottom of the container, resulting in a high resin content in the sprayed paint and a lighter color.

② Wrong spraying technique. For example, each subsequent coat was not reapplied, resulting in stripes or poor coverage.

③ Too much thinner is used, making the paint coating very thin.

④The old paint layer or the bottom coating contains pigments that can cause color bleeding, so the old paint layer should be handled carefully, and an isolation layer that can prevent color bleeding can be sprayed.

(2) Correction method:

If there is slight bleeding, spray enough paint to cover. Severe bleeding paint should be sanded off and repainted.

[9] cracking of putty or primer

In the paint repair area, the putty-filled area or the primer layer cracks, resulting in cracking of the topcoat layer.

(1) Cause

① The putty layer or the primer layer is too thick, and the drying time between each layer is insufficient, so that the surface of the putty layer or the primer layer is dry and the bottom layer is soft, resulting in cracking of the putty layer or the primer layer. Therefore, in the putty scraping or primer spraying, the method of thin-layer construction should be adopted for multiple times, and sufficient drying time should be allowed according to the climatic conditions.

②The transition area between the putty or middle coat primer layer and the old paint layer, that is, the treatment around the feather edge is not sufficient, resulting in the loose combination of the putty coating and cracking. 600 grit sandpaper should be used to avoid bringing the solvent into the The deep scraping layer of the lower layer.

③ The use of unsatisfactory thinners in the primer will cause the primer layer to not easily dry or shrink excessively and crack.

(2) Correction method:

Sand cracked areas thoroughly, re-scrape putty and apply primer and topcoat, taking care to allow adequate drying time between coats.

【10】Small cracks

The paint surface is severely tarnished, and there are many small cracks on the topcoat layer, similar in shape to the cracks in the soil in a dried-up pond, and the cracks often take the form of triangles, stars or irregular radiating shapes. Cracking generally occurs in the topcoat layer, but sometimes penetrates deep into the inner coat.

(1) Cause

①The paint layer is too thick. An excessively thick topcoat will amplify the normal stress and cause cracking, and a thinner coating should be sprayed multiple times. Moreover, sufficient drying time should be allowed between each topcoat spraying operation, and it should not be dried with a spray gun.

②The wrong additive was used. The instructions on the paint label should be carefully read and strictly followed, as various additives that are not specific to the topcoat layer will damage the final paint layer and make the finish more prone to cracking.

(2) Correction method:

If the crack cannot be removed by grinding and polishing, the cracked part should be thoroughly polished. In severe cases, the paint layer should be removed until the metal layer is exposed and re-sprayed.

【11】Linear crack

The surface of the topcoat has obvious linear crack penetration, and the cracks are relatively parallel. It is most common on black or other dark paint surfaces.

(1) Cause

①The rough sandpaper was used for surface treatment. The correct way is to use finer sandpaper than the last one for each sanding.

② Improper use of thinners, too strong solubility, should use thinners compatible with the paint.

③The old paint surface or the previous repaired surface is not fully treated, and the original cracks have traces that have not been removed. This phenomenon often occurs when a new paint layer is sprayed on the original cracked paint layer, so the paint surface is repaired. The repaired area should be thoroughly cleaned.

(2) Correction method:

Use the correct primer and topcoat for old paint and substrates, if cracks appear, smooth the surface with fine-grit sandpaper to expose the undercoat and re-spray with the correct thinner.

【12】Brittle crack

Also known as tears or claw marks, cracks appear as irregular lines that extend outward.

(1) Cause

① During the spraying process, the paint layer is sprayed too thickly, resulting in the total thickness of the old paint layer and the new paint layer being too large and cracks appear. Therefore, the practice of multiple spraying with thinner coatings should be strictly followed to achieve the correct coating thickness.

②The paint layer is too thin, especially the topcoat layer is too thin, which will cause the paint layer to crack or fall off prematurely.

③ The paint quality is too poor, or the paint surface is exposed to sunlight for a long time, or the chemical substances in the atmospheric environment cause erosion of the paint surface, which will lead to cracks.

④The influence of old paint layer or previous repairing. Make sure that the topcoat matches the base coat and that the old coat of paint in the base coat is not too thick.

⑤ Ensure the fusion of the old paint layer and the new spray paint layer. Factors such as climatic conditions and the thickness of the paint layer will affect the drying time of the paint layer, so the construction cannot be absolutely based on the drying time, and should be flexibly controlled.

⑥ The paint is not fully stirred or sprayed with partially gelled paint. If the paint is not stirred evenly, the additives in the paint cannot fully function, and the stress resistance of the paint surface is weakened, and cracks will appear.

⑦The paint is sprayed on the surface that is too cold, such as the surface of one-component acrylic varnish

(2) Correction method:

Thoroughly sand the cracked area to the primer layer and re-spray. In severe cases, the paint layer should be removed until the metal layer is exposed and re-sprayed.

[13] Sandpaper trace expansion

There are obvious sanding marks on the paint surface.

(1) Cause

①The bottom layer is sanded with coarser sandpaper, and the sandpaper marks are not filled with putty or primer.

② Improper thinner or thinner ratio is used, the thinner in the freshly sprayed topcoat will penetrate into the old paint layer, which will expand the sandpaper marks.

(2) Correction method:

Sand paper marks dry or wet until smooth, then scrape putty and spray primer and topcoat.

【14】White fog

Also known as fogging or surface dulling, which can appear milky on the surface of the paint during or shortly after spraying

Hazy appearance, which is only seen on one-pack acrylic clear coats.

(1) Cause

①The appearance of white fog is often related to bad weather. In high temperature or cold and humid weather, the solvent in the paint volatilizes rapidly, causing the temperature of the paint surface to drop. At this time, the moisture in the air condenses on the surface of the paint layer, resulting in white fog. The use of poor quality thinners, cold weather or too fast air movement can cause white fog to appear, as can spot repairs.

②Use the wrong thinner. The use of fast evaporating thinners can cause excessive cooling of thick paint films, resulting in condensation of airborne moisture on the paint surface.

③ Improper adjustment of spray gun or compressed air. If the compressed air pressure is too high, it will also cool the wet paint surface, increasing the rate of moisture condensation.

④ Improper drying. Forcibly drying the paint surface with a spray gun will speed up the evaporation of the thinner in the paint film, resulting in the condensation of water.

(2) Correction method:

Repaint in a proper working environment.