Causes of paint blisters or prickly heat and preventive measures
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Blistering or prickly heat on the paint
 
Related instructions

 
Blisters refer to the appearance of round protrusions of different sizes in the paint film. For defects that are dense and numerous, similar to the prickly heat that appears on the human body in hot and humid weather, it is called prickly heat. When we carefully observe such defects, we will find that this kind of defect is actually a part of the coating film bulging upwards from the coated surface or the primer layer, so it is very difficult to handle. This kind of bulge contains moisture or air inside, and its size The diameter is between 0.5 mm and 5 mm. Most of the time, they appear in pieces, and rarely appear alone. Generally speaking, the chances of appearing in the topcoat layer are far more than those between the paint and the substrate. The bottom line is that moisture or dirt is trapped under the paint film.

 
Generally speaking, solvent bubbles or stirring air bubbles due to bottom surface contamination or insufficient cleaning, tool contamination or poor spraying environment or unsuitable curing agent or thinner will appear at the same time as spraying, while the foaming defects caused by water vapor are generally Appears from a few minutes to a month after spraying.

 
Under normal circumstances, it is unavoidable that gas, or even water vapor, will be mixed into the coating during the coating process. For example: the air entering during the stirring process is not sufficiently static and defoaming, the compressed air brought in during the spraying process, the air and water vapor absorbed by the porous substrate or the wet substrate, etc. But these bubbles should be able to be eliminated by the coating itself during the drying process, but sometimes the reasons for the bubbles are various, and it is difficult to explain with a single mechanism. But the basic principle of bubble generation is the following process. Under normal circumstances, after spraying, the coating can rise to the surface of the paint film due to the action of surface tension in the process of forming the paint film. When heated, the bubbles rise and expand until the surface Cracked, and then leveled to get a smooth paint film. Therefore, in the above-mentioned links, no matter which link is abnormal, it will affect the disappearance of the bubbles. In the process of film formation, the solvent volatilizes too fast, the viscosity of the paint liquid rises too fast, and the increase of surface tension is not conducive to defoaming and leveling.

 
Related reasons
 
1. When the paint film is in a high humidity environment or immersed in water, due to the penetration of moisture into the film, when its vapor pressure reaches a sufficient level, foaming will occur. Sun exposure can accelerate this phenomenon.

 
2. Improper cleaning of the bottom surface. When a new primer is applied by water grinding, the water quality of the last water used to clean the coated surface is poor because the salt contained in the wet grinding water remains between the metal and the primer or the primer and the topcoat, and contains impurity ions and deposits on the surface. Water on the surface, or when wet grinding is not completely dry, is enough to cause blistering. In addition, if gasoline is used to clean the bottom surface, such defects are also very likely to occur due to the presence of water-soluble additives or impurities contained in gasoline.

 
3. The materials used are not matched, or the thinner is not used as specified. Influence of improper dilution ratio or poor diluent. Poor quality, too fast-drying thinner and insufficient dilution ratio, too high air pressure from the spray gun, and dry spraying of the primer causing the primer film to become porous are all sufficient to cause air bubbles. The water content of the thinner used in baking paint must not exceed 0.5%, but generally the water content of nitro thinner is relatively high. When spraying 2K type baking paint, nitro thinner cannot be used. Special attention should be paid to the combination of too high gun pressure and too fast drying thinner, which can easily cause air or water vapor ash to be trapped in the paint film.

 
4. The paint film is too thick. Insufficient drying time and overspray of the primer are sufficient to keep the solvent in the primer from evaporating. This problem generally occurs in spraying when the interval between two sprays is insufficient or the solvent volatilization time after spraying is too short, and the forced heating is too fast and premature. The failures caused by this reason generally have a more obvious feature: the planes are many and heavy, and the facades are less and lighter. Because this is related to the thickness of the coating, it is easier to get a thicker paint film on a flat surface.

 
5. Water-soluble impurities, oil and dirt from air or air ducts, factory tools, old paint, etc. that cause foaming.

 
6. The influence of some inferior primer and putty. We have learned that there are some extremely low-priced primers and putties on the market, which use excessive fillers to reduce costs. These primers or putties have extremely poor water resistance. When the ambient humidity is too high, they will Causes the absorption of environmental moisture, and then returns to the topcoat to form prickly heat or blistering.

 
7. Improper use of additives. Additives added to topcoats or primers to prevent various problems can seriously impair foam resistance.

 
8. Effects of old paint or previous repairs. Contamination of old paint or previously repaired surfaces can also cause blistering problems. Such as polishing wax, detergent or other materials.

 
9. Wet-grinding polyester putty, after wet-grinding, absorbs or retains water vapor in the micropores, which will also cause foaming problems. After water-grinding the putty, it should be dried with compressed air and then allowed to stand for 1 hour at room temperature before spraying the primer.

 
10. The topcoat is sprayed directly without filling and sealing with a primer after the putty or eye filler is ground, so that the air and moisture existing in the microporous defects of the substrate enter into the coating and cause foaming defects. Of course, the scraping technology of putty also sometimes affects the generation of air bubbles. Poor scraping technology will seal a large amount of air in the putty, so it is necessary to master the correct scraping technology of putty.

 
11. Paint before the gas mixed into the paint is released during stirring. Usually, we recommend adding curing agent and diluent to the paint and stirring thoroughly, then let it stand for 5-10 minutes before painting.

 
12. The temperature of the spraying environment is too high, or the air flow is too fast.

 
13. The spraying air pressure is too low or too high, the flash-off time between passes is too short, the temperature rises too quickly after spraying, or the heating source is too close to the paint surface.

 
14. Polyurethane coatings containing isocyanates react with moisture in the air to produce carbon dioxide gas. Therefore, spraying in a high temperature and high humidity environment, using high solid paint thick coating, polyurethane paint is easy to generate air bubbles.

 
Precaution
 
1. For construction in high temperature and high humidity climate conditions, it is necessary to add some (generally no more than 5% of the total) high-boiling point solvent to the topcoat in advance, which can slow down the surface drying speed of the paint film and make the solvent in the coating sufficient. volatilize to avoid excess accumulation of solvent. At the same time, the volatilization intensity is reduced, so that the surface of the coating film will not be rapidly cooled and the difference with the ambient temperature is too large.

 
2. All surfaces must be clean and free of contamination, and no hydrophilic substances are allowed to remain.

 
3. The grinding water needs to be replaced frequently, and all the grinding dirt should be removed. The last wash should be deionized water or distilled water. If using tap water, be sure to wipe and blow dry with a clean cloth, then dry.

 
4. The dried surface cannot be wiped on it by hand.

 
5. Compressed air and topcoat should be clean and free from contamination.

 
6. The primer or topcoat should be sprayed to an appropriate thickness.

 
7. Sufficient drying time should be left between each layer to allow enough time for the solvent in the middle to evaporate.

 
8. The coating must be allowed to dry sufficiently before being exposed to humidity and high temperature.

 
9. For occasions where a large number of painting operations are carried out throughout the year, it is recommended to install an effective freeze dryer. Drain the air compressor tank daily.

 
remedy
 
Puncture the bubble with a needle to determine the depth of the bubble and use a low magnification magnifying glass to find the cause of the bubble. When air bubbles occur between paint layers, the defective area can be sanded off to expose the intact paint layer before repainting. If the defect is serious, or bubbles occur between the primer and the substrate, the paint layer on the substrate should be completely removed, and then repainted. In fact, blistering is a difficult problem to deal with. To some extent, it is more troublesome than biting the bottom, because this problem may still occur after continuous coating for many times. Bubbles are generally destructive defects of the coating. Reprocessing, in most cases, can only be removed, re-surface preparation, putty scraping or primer spraying.

 
Ø Slight blistering and prickly heat can be dealt with by the following methods: Polish with soapy water until smooth, seal with two-component secondary primer, and re-spray with secondary paint after drying.

 
Ø If the damage area is extensive and its depth reaches the primer layer, the paint should be removed to the primer or metal surface and then re-applied.

 

Common problems and preventive measures in the application of real stone paint
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Real stone paint has the characteristics of strong decoration, wide application, good durability and not easy to fade, so it is a kind of popular exterior wall decorative paint. In the construction and application of real stone paint, there are often some problems affecting the quality and decorative effect, which are universal to a certain extent. These problems are sometimes caused by improper selection of raw materials and formulation design, while others are caused by incorrect construction methods. This paper discusses the solution to these problems from the perspective of formulations and materials.

 

1. The coating is too soft

 
The coating of good-quality real stone paint should be very hard, and the nails cannot be pulled. If you can still scratch with your nails three days after application in good weather, the coating should be considered too soft. The main reason that the real stone paint is too soft is that the selected emulsion is not appropriate. Many manufacturers use the same emulsion as latex paint when preparing real stone paint, which is wrong. The emulsion content in the real stone paint formulation is low, and the coating is not tight enough due to the presence of a large amount of sand and gravel during film formation. Therefore, an emulsion with higher cohesion and a higher minimum film-forming temperature should be selected.

 
According to research, the adhesive strength of the emulsion used for the preparation of real stone paint should not be lower than 3MPa, and the minimum film-forming temperature should not be lower than 20 degrees Celsius. The higher minimum film-forming temperature may cause the disadvantage that the film is not easy to form when the temperature is low, which can be solved by appropriately adding more film-forming additives. Coalescent additives can be completely volatilized after the coating is dried, and generally do not affect the performance of the coating. At present, alcohol-12, which is used more in the production of water-emulsion paints, also has good results when used in real stone paints. The dosage is generally five parts in one hundred parts of the emulsion.

 

2. The coating turns white when exposed to water

 
The acrylate emulsion used as a film-forming aid for real stone paint should have good water resistance after drying, so the coating should not turn white when exposed to water after drying. However, some real stone paint coatings will turn white after each rain, and the coating will become loose, and after the rain stops, the coating will return to its original color after exposure to the sun. After analysis, this is caused by the poor water resistance of the coating and the absorption of water. From the analysis of the structure of polyacrylate, the real stone paint coating should have good water resistance. However, since the acrylic emulsion needs to be added with surfactants during the synthesis, some manufacturers use a large amount of surfactants in order to increase the stability of the emulsion; some manufacturers add carboxymethyl cellulose and hydroxyethyl cellulose when preparing real stone paint and other substances as thickeners, and sodium benzoate was added as a preservative. These substances are all water-soluble or hydrophilic, and they remain in the coating after film formation, which greatly reduces the water resistance of the coating. The experiment shows that the water absorption rate of the coating formed by mixing pure acrylic emulsion and quartz sand without any additives by spraying is 0.42%; and adding 0.4% hydroxyethyl cellulose on the basis of the above coating, the water absorption rate increases to 4.3%. Since the coating of real stone paint is thick, once it absorbs water, it is not easy to be released in a short time, resulting in white appearance and loose coating inside.

 
To solve the above problems, raw materials and formulations can be improved. First of all, you should choose an emulsion with excellent quality. The silicone-modified acrylate emulsion (silicone-acrylic emulsion) developed in recent years has good hydrophobicity and can effectively resist the intrusion of water. Secondly, special thickeners should be selected. The thickening effect of the thickener is good and the dosage is small, so it will not cause a large change in the coating properties. At present, there are many thickeners available on the market, such as Henkel Corporation of Germany and Deqian Corporation of Taiwan Province. Preservatives should also choose special materials.

 
Recently, the silicone waterproofing liquid currently available in the Shanghai market was added to the real stone paint, and unexpected good results were received. Rainwater rolls down on the surface of the coating in the form of beads without penetrating into the coating, which makes the real stone paint both decorative and waterproof.

 

 
3. Too much sand is dropped when spraying

 
Some real stone paints lose a lot of sand during spraying, which can reach about 1/3 in severe cases, causing waste. In addition to the reasons for the construction method, raw materials and formulations may also cause the above phenomenon. At present, there are two kinds of sand used for real stone paint, artificial sand and natural sand. It has been observed that the real stone paint prepared with natural sand has less damage than when using artificial sand. This may be related to the hardness and surface state of the sand. Generally speaking, it is easy to lose sand when using sand with higher hardness and a more compact and smooth surface. In addition, when preparing real stone paint, the gradation of sand is also important. Properly graded real stone paint not only has less sand loss during spraying, but also has a tighter coating. Therefore, it is recommended to use natural sand as much as possible when preparing real stone paint, and make the sand have a certain gradation. Studies have shown that with the following gradation, less sand is lost during construction, and the quality of the coating is also better: 5% of the particle size is larger than 10 mesh, 25% between 10-15 mesh, 50% between 50-100 mesh, and less than 100 mesh. Purpose 20%.

 
In addition, the consistency of the coating also has a certain influence on the sand drop phenomenon during spraying. If the coating is too thick, it will be difficult to construct, and if it is too thin, the initial viscosity of the sand will be too low when it is applied to the wall, which will cause the sand to fall. Therefore, in the case of no difficulty in construction, the consistency of the coating should be improved as much as possible, which will help to solve the problem of sand loss.

Causes and preventive measures of pinholes
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pinhole

 
Related instructions:

 
A pinhole is a very small hole that penetrates the entire paint film like a pinhole, which will reduce the airtightness of the paint film and allow external moisture to penetrate the paint film to the substrate. Pinholes are caused by solvents or moisture that dries out on the surface of the paint film and cannot volatilize these solvents or moisture in the primer or topcoat. Pinholes are more prone to pinholes in drying-type paints (including two-component self-drying polyurethane paints). Pinholes mostly appear on planes, and vertical planes rarely occur.

 
Related reasons

 
1. The substrate is rough and has pores.

 
2. Too little thinner is added or bad thinner is used. Solvents with too low boiling points or added too little will dry the paint film too quickly. The moisture of the thinner material exceeds the standard, and the moisture will react with the two-component polyurethane curing agent to generate C02 gas, resulting in pinholes.

 
3. The paint film is coated too thickly, the interior of the paint film does not have enough drying time before the surface dries, and the internal solvent volatilizes to cause pinholes. In high temperature weather construction, the interval between layers is too short, and pinholes will also appear.

 
4. The flashing time after spraying is not enough, that is, heating up to accelerate drying.

 
Precaution:

 
1. The surface of the porous material is closed before further construction. For example, the putty must be sprayed with gray primer.

 
2. Use matching thinners and add them in proportion.

 
3. For the parts that need thick coating, such as the hood, it can be sprayed in three times, and the interval between the first two coats can be appropriately extended, and the topcoat can be further diluted before the last coat.

 
4. Allow at least 15 minutes to flash dry before accelerating drying, or heat up and bake after surface drying.

 
remedy

 
Thoroughly sand the topcoat where the pinholes appear, then reapply.

Causes of paint blisters or prickly heat and preventive measures
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Blistering or prickly heat on the paint
 
 

 
Related instructions
 
Blisters refer to the appearance of round protrusions of different sizes in the paint film. for defects

It is dense and numerous, similar to the prickly heat that appears on the human body in hot and humid weather, which is called prickly heat. When we carefully observe such defects, we will find that this kind of defect is actually a part of the coating film bulging upwards from the coated surface or the primer layer, so it is very difficult to handle. This kind of bulge contains moisture or air inside, and its size The diameter is between 0.5 mm and 5 mm. Most of the time, they appear in pieces, and rarely appear alone. Generally speaking, the chances of appearing in the topcoat layer are far more than those between the paint and the substrate. The bottom line is that moisture or dirt is trapped under the paint film.

 
Generally speaking, solvent bubbles or stirring air bubbles due to bottom surface contamination or insufficient cleaning, tool contamination or poor spraying environment or unsuitable curing agent or thinner will appear at the same time as spraying, while the foaming defects caused by water vapor are generally Appears from a few minutes to a month after spraying.

 
Under normal circumstances, it is unavoidable that gas, or even water vapor, will be mixed into the coating during the coating process. For example: the air entering during the stirring process is not sufficiently static and defoaming, the compressed air brought in during the spraying process, the air and water vapor absorbed by the porous substrate or the wet substrate, etc. But these bubbles should be able to be eliminated by the coating itself during the drying process, but sometimes the reasons for the bubbles are various, and it is difficult to explain with a single mechanism. But the basic principle of bubble generation is the following process. Under normal circumstances, after spraying, the coating can rise to the surface of the paint film due to the action of surface tension in the process of forming the paint film. When heated, the bubbles rise and expand until the surface Cracked, and then leveled to get a smooth paint film. Therefore, in the above-mentioned links, no matter which link is abnormal, it will affect the disappearance of the bubbles. In the process of film formation, the solvent volatilizes too fast, the viscosity of the paint liquid rises too fast, and the increase of surface tension is not conducive to defoaming and leveling.

 
Related reasons
 
1. When the paint film is in a high humidity environment or immersed in water, due to the penetration of moisture into the film, when its vapor pressure reaches a sufficient level, foaming will occur. Sun exposure can accelerate this phenomenon.

 
2. Improper cleaning of the bottom surface. When a new primer is applied by water grinding, the water quality of the last water used to clean the coated surface is poor because the salt contained in the wet grinding water remains between the metal and the primer or the primer and the topcoat, and contains impurity ions and deposits on the surface. Water on the surface, or when wet grinding is not completely dry, is enough to cause blistering. In addition, if gasoline is used to clean the bottom surface, such defects are also very likely to occur due to the presence of water-soluble additives or impurities contained in gasoline.

 
3. The materials used are not matched, or the thinner is not used as specified. Influence of improper dilution ratio or poor diluent. Poor quality, too fast-drying thinner and insufficient dilution ratio, too high air pressure from the spray gun, and dry spraying of the primer causing the primer film to become porous are all sufficient to cause air bubbles. The water content of the thinner used in baking paint must not exceed 0.5%, but generally the water content of nitro thinner is relatively high. When spraying 2K type baking paint, nitro thinner cannot be used. Special attention should be paid to the combination of too high gun pressure and too fast drying thinner, which can easily cause air or water vapor ash to be trapped in the paint film.

 
4. The paint film is too thick. Insufficient drying time and overspray of the primer are sufficient to keep the solvent in the primer from evaporating. This problem generally occurs in spraying when the interval between two sprays is insufficient or the solvent volatilization time after spraying is too short, and the forced heating is too fast and premature. The failures caused by this reason generally have a more obvious feature: the planes are many and heavy, and the facades are less and lighter. Because this is related to the thickness of the coating, it is easier to get a thicker paint film on a flat surface.

 
5. Water-soluble impurities, oil and dirt from air or air ducts, factory tools, old paint, etc. that cause foaming.

 
6. The influence of some inferior primer and putty. We have learned that there are some extremely low-priced primers and putties on the market, which use excessive fillers to reduce costs. These primers or putties have extremely poor water resistance. When the ambient humidity is too high, they will Causes the absorption of environmental moisture, and then returns to the topcoat to form prickly heat or blistering.

 
7. Improper use of additives. Additives added to topcoats or primers to prevent various problems can seriously impair foam resistance.

 
8. Effects of old paint or previous repairs. Contamination of old paint or previously repaired surfaces can also cause blistering problems. Such as polishing wax, detergent or other materials.

 
9. Wet-grinding polyester putty, after wet-grinding, absorbs or retains water vapor in the micropores, which will also cause foaming problems. After water-grinding the putty, it should be dried with compressed air and then allowed to stand for 1 hour at room temperature before spraying the primer.

 
10. The topcoat is sprayed directly without filling and sealing with a primer after the putty or eye filler is ground, so that the air and moisture existing in the microporous defects of the substrate enter into the coating and cause foaming defects. Of course, the scraping technology of putty also sometimes affects the generation of air bubbles. Poor scraping technology will seal a large amount of air in the putty, so it is necessary to master the correct scraping technology of putty.

 
11. Paint before the gas mixed into the paint is released during stirring. Usually, we recommend adding curing agent and thinner to the paint and stirring thoroughly, then let it stand for 5-10 minutes before painting.

 
12. The temperature of the spraying environment is too high, or the air flow is too fast.

 
13. The spraying air pressure is too low or too high, the flash-off time between passes is too short, the temperature rises too quickly after spraying, or the heating source is too close to the paint surface.

 
14. Polyurethane coatings containing isocyanates react with moisture in the air to produce carbon dioxide gas. Therefore, spraying in a high temperature and high humidity environment, using high solid paint thick coating, polyurethane paint is easy to generate air bubbles.

 
Precaution
 
1. For construction in high temperature and high humidity climate conditions, it is necessary to add some (generally no more than 5% of the total) high-boiling point solvent to the topcoat in advance, which can slow down the surface drying speed of the paint film and make the solvent in the coating sufficient. volatilize to avoid excess accumulation of solvent. At the same time, the volatilization intensity is reduced, so that the surface of the coating film will not be rapidly cooled and the difference with the ambient temperature is too large.

 
2. All surfaces must be clean and free of contamination, and no hydrophilic substances are allowed to remain.

 
3. The grinding water needs to be replaced frequently, and all the grinding dirt should be removed. The last wash should be deionized water or distilled water. If using tap water, be sure to wipe and blow dry with a clean cloth, then dry.

 
4. The dried surface cannot be wiped on it by hand.

 
5. Compressed air and topcoat should be clean and free from contamination.

 
6. The primer or topcoat should be sprayed to an appropriate thickness.

 
7. Sufficient drying time should be left between each layer to allow enough time for the solvent in the middle to evaporate.

 
8. The coating must be allowed to dry sufficiently before being exposed to humidity and high temperature.

 
9. For occasions where a large number of painting operations are carried out throughout the year, it is recommended to install an effective freeze dryer. Drain the air compressor tank daily.

 
remedy
 
Puncture the bubble with a needle to determine the depth of the bubble and use a low magnification magnifying glass to find the cause of the bubble. When air bubbles occur between paint layers, the defective area can be sanded off to expose the intact paint layer before repainting. If the defect is serious, or bubbles occur between the primer and the substrate, the paint layer on the substrate should be completely removed, and then repainted. In fact, blistering is a difficult problem to deal with. To some extent, it is more troublesome than biting the bottom, because this problem may still occur after continuous coating for many times. Bubbles are generally destructive defects of the coating. Reprocessing, in most cases, can only be removed, re-surface preparation, putty scraping or primer spraying.

 
Ø Slight blistering and prickly heat can be dealt with by the following methods: Polish with soapy water until smooth, seal with two-component secondary primer, and re-spray with secondary paint after drying.

 
Ø If the damage area is extensive and its depth reaches the primer layer, the paint should be removed to the primer or metal surface and then re-applied.

 
Q WE

Causes and preventive measures of sagging
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Sagging

 
Related claims

 
Drooping, hanging paint.

 
Related instructions

 
When painting on a vertical surface, some paints may flow under the action of gravity. Note: Sagging can be caused by the appearance of a curtain-like paint film caused by paint falling on the entire vertical surface, also known as curtain-shaped sagging; it can also be caused by excessive paint in local slits or nail holes. It is called sagging; tear sagging is a special form of sagging.

 
cause

 
1. Continuous spraying that is too thick and too wet is the most common cause of sagging.

 
2. The temperature of the construction site is too low, and the thin material volatilizes too slowly.

 
3. The interval between layers is too short.

 
4. The spray gun is too close to the paint film, and the wind speed causes the flow of the wet paint film.

 
5. Improper dilution ratio. Too much thinner makes the coating viscosity too low and reduces sag resistance.

 
Prevention points

 
1. The flow has an interlayer interval of 10-15 minutes.

 
2. During construction in winter, appropriately reduce the amount of thinner and appropriately extend the interval between layers.

 
3. Learn and apply proper painting techniques.

 
4. Use suitable paint and use it in proportion.

 
Solution

 
1. For slight sagging, after the paint film is completely dry, use sandpaper above 1000 grit to water and then polish.

 
2. For the paint surface with serious sagging problem, it should be re-sanded after thorough drying, cleaned and re-sprayed.

 

The Causes, Preventions, and Solutions of 8 Common Paint Malfunctions
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There are many unknown and possible ills in coating construction, and these ills have their own unique triggering factors. The following will introduce the causes, preventive measures and solutions of 8 kinds of ills.

 
1. Flowering

 
--During the storage or drying process of color paints containing a mixture of different pigments, one or more pigments are separated or floated, and the surface of the color paint or paint film concentrates on the appearance of uneven color streaks or spots.

 
Answer: Reason analysis: ① Poor dispersion of pigments, resulting in pigment separation; ② Paint drying too fast; ③ Improper use of surface additives. Preventive measures: ① Make sure the pigment is well dispersed; ② Use slow drying solvent and make sure to use the correct diluent; ③ Use wax or oil repellant; ④ One application should not be too thick.

 

2. Metallic paint blooms

 
--Specially refers to the phenomenon of uneven color caused by uneven distribution or arrangement of metal powder during the construction of metallic paint.

 
Answer: Analysis of the reasons: ① The construction shot is uneven; ② The spraying is too wet; ③ Poor thinner is used; ④ The spray pressure is wrong; ⑤ The paint itself is not good in construction. Preventive measures: ① Use the correct gun mode and air pressure; (generally, the air pressure is slightly larger, the spray width is slightly larger, and the gun is fast and not easy to flower); ② Slightly dry spray; ③ Use correct diluent.

 

3. Blistering prickly heat

 
--Bubble of air or solvent vapor, or both, formed during the coating construction process, which can disappear or exist permanently during the drying process of the paint film.

 
Answer: Analysis of the reasons: ① Incorrect brushing method, or paint that is not suitable for brushing construction is applied by brushing; ② The paint has insufficient wetting ability to the substrate, or the substrate is not treated cleanly; ③ The solvent evaporates too quickly ( Use too fast thinner or too fast heating); ④ Single-layer construction is too thick or (and) the interval between each coat is too short; ⑤ The polyurethane paint contains moisture; Preventive measures: ① Operate strictly according to the instructions; ② Clean the substrate; ③ Use appropriate surface additives; ④ Spray wet film should have enough flash time, and thick wet film should have longer flash time before baking; ⑤ Avoid applying or (and) drying the paint at lower temperatures. *Note: "Prickly heat", the shape of "prickly heat" is very similar to that of bubbles, but generally smaller, and the causes are also similar and slightly different. The main causes of prickly heat are: ① The paint has insufficient wetting ability to the substrate, or The substrate is not cleanly treated; ② The solvent evaporates too quickly (use too fast thinner or heat too quickly); ③ Single-layer construction is too thick or (and) the interval between each coat is too short; ④ The polyurethane paint contains moisture or is wet Drying in the environment; ⑤It is easy to appear when the baking paint is applied and dried below 5℃; *The formation of prickly heat is more complicated. The most likely causes of prickly heat are solvent retention and moisture. Baking paint is prone to prickly heat due to its strong solvent retention ability. In a higher temperature environment, violent solvent volatilization and strong deep agent retention will cause Causes the solvent vapor to stay in the paint film, thereby forming prickly heat. At low temperature, the wet paint film has poor fluidity, especially the surface temperature is low due to solvent volatilization, and the fluidity is worse, which is more suitable for solvent vapor retention, and moisture is also easy to cause Prickly heat, the moisture in the paint and the moisture in the construction environment cause prickly heat evenly, while the prickly heat caused by the erosion of the paint film by moisture is often uneven and has a certain pattern like insects crawling. Preventive measures: ①Improve the dryness of the paint film, thereby improving the solvent release of the paint film; ②Avoid construction drying at low temperature ③Reduce the polarity of the solvent, thereby reducing the solvent retention ability of the paint film; Surface air permeability; ⑤ Use the correct diluent and curing agent.

 

4. Pinhole

 
--A pathological condition that resembles pinholes in the paint film.

 
Answer: It is caused by the rupture of air bubbles mixed in the wet paint film and other generated bubbles, and it cannot be leveled before the paint film is dried (cured). It should also be caused by improper substrate treatment or trial coating (the paint film is too thick etc.) caused. Pinhole drying paints are more prone to pinholes (including two-component self-drying polyurethane paints). A pinhole is a very small hole that penetrates the entire paint film like a pinhole, which will reduce the airtightness of the paint film and allow external moisture to penetrate the paint film to the substrate. Reason analysis: ① The substrate, paint or thinner contains moisture. (Moisture will react with the two-component polyurethane curing agent to generate C02 gas); ②The substrate is rough and has pores. ③ Too much low-boiling point solvent or too much desiccant is added to the paint; ④ The paint film is too thick to dry the outside and the inside, and the internal solvent volatilizes to cause pinholes;

 

 
5. Orange peel

 
- The paint film exhibits a superficial morbidity with an orange peel-like appearance. This morbidity is prone to occur during spraying construction (especially when the substrate is flat).

 
 Sagging

 
--When the paint is applied on a vertical surface, the wet paint film moves downward due to its poor sag resistance or improper application, and the paint film is too thick, forming uneven coatings with thick lower edges of various shapes.

 
Answer: Note: Sag can be caused by the paint falling on the entire vertical surface, which is similar to the appearance of curtain-like paint film, also known as curtain-like sagging; it can also be caused by excessive paint in local slits or nail holes. , also known as sagging; tear sagging is a special form of sagging.

 

6. Bite the bottom

 
- When the same or different kinds of coatings are applied on the dry paint film, during the coating application or drying, the underlying dry paint film softens, swells or detaches from the substrate (usual appearance such as wrinkling) .

 
Answer: Reason analysis: ①Apply the topcoat before the primer is dry. ②The primer is oil-based, such as alkyd, the topcoat has strong solvent solubility and the coating is too thick. ③Fiber

Vitamin self-drying paint or self-drying acrylic paint over other paints that are completely dry. ④ The primer has a general solvent dissolving ability, and the topcoat has a strong solvent dissolving ability. ⑤ The bottom and top paint are not matched.

 

7. Bleeding

 
- The diffusion process of colored substances from the lower layer (substrate or primer) into and through the upper paint film, thus causing the paint film to exhibit undesired coloring or fringing.

 
Answer: Reason analysis: ①The color of the primer is too dark, and the color of the topcoat is too light. ②The primer is not completely dry. ③The primer contains more migratory pigments, such as red pigments.

 

Causes and preventive measures of paint not drying or poor drying
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Blistering or prickly heat on the paint
 
 

 
Related instructions
 
Blisters refer to the appearance of round protrusions of different sizes in the paint film. For defects that are dense and numerous, similar to the prickly heat that appears on the human body in hot and humid weather, it is called prickly heat. When we carefully observe such defects, we will find that this kind of defect is actually a part of the coating film bulging upwards from the coated surface or the primer layer, so it is very difficult to handle. This kind of bulge contains moisture or air inside, and its size The diameter is between 0.5 mm and 5 mm. Most of the time, they appear in pieces, and rarely appear alone. Generally speaking, the chances of appearing in the topcoat layer are far more than those between the paint and the substrate. The bottom line is that moisture or dirt is trapped under the paint film.

 
Generally speaking, solvent bubbles or stirring air bubbles due to bottom surface contamination or insufficient cleaning, tool contamination or poor spraying environment or unsuitable curing agent or thinner will appear at the same time as spraying, while the foaming defects caused by water vapor are generally Appears from a few minutes to a month after spraying.

 
Under normal circumstances, it is unavoidable that gas, or even water vapor, will be mixed into the coating during the coating process. For example: the air entering during the stirring process is not sufficiently static and defoaming, the compressed air brought in during the spraying process, the air and water vapor absorbed by the porous substrate or the wet substrate, etc. But these bubbles should be able to be eliminated by the coating itself during the drying process, but sometimes the reasons for the bubbles are various, and it is difficult to explain with a single mechanism. But the basic principle of bubble generation is the following process. Under normal circumstances, after spraying, the coating can rise to the surface of the paint film due to the action of surface tension in the process of forming the paint film. When heated, the bubbles rise and expand until the surface Cracked, and then leveled to get a smooth paint film. Therefore, in the above-mentioned links, no matter which link is abnormal, it will affect the disappearance of the bubbles. In the process of film formation, the solvent volatilizes too fast, the viscosity of the paint liquid rises too fast, and the increase of surface tension is not conducive to defoaming and leveling.

 
Related reasons
 
1. When the paint film is in a high humidity environment or immersed in water, due to the penetration of moisture into the film, when its vapor pressure reaches a sufficient level, foaming will occur. Sun exposure can accelerate this phenomenon.

 
2. Improper cleaning of the bottom surface. When a new primer is applied by water grinding, the water quality of the last water used to clean the coated surface is poor because the salt contained in the wet grinding water remains between the metal and the primer or the primer and the topcoat, and contains impurity ions and deposits on the surface. Water on the surface, or when wet grinding is not completely dry, is enough to cause blistering. In addition, if gasoline is used to clean the bottom surface, such defects are also very likely to occur due to the presence of water-soluble additives or impurities contained in gasoline.

 
3. The materials used are not matched, or the thinner is not used as specified. Influence of improper dilution ratio or poor diluent. Poor quality, too fast-drying thinner and insufficient dilution ratio, too high air pressure from the spray gun, and dry spraying of the primer causing the primer film to become porous are all sufficient to cause air bubbles. The water content of the thinner used in baking paint must not exceed 0.5%, but generally the water content of nitro thinner is relatively high. When spraying 2K type baking paint, nitro thinner cannot be used. Special attention should be paid to the combination of too high gun pressure and too fast drying thinner, which can easily cause air or water vapor ash to be trapped in the paint film.

 
4. The paint film is too thick. Insufficient drying time and overspray of the primer are sufficient to keep the solvent in the primer from evaporating. This problem generally occurs in spraying when the interval between two sprays is insufficient or the solvent volatilization time after spraying is too short, and the forced heating is too fast and premature. The failures caused by this reason generally have a more obvious feature: the planes are many and heavy, and the facades are less and lighter. Because this is related to the thickness of the coating, it is easier to get a thicker paint film on a flat surface.

 
5. Water-soluble impurities, oil and dirt from air or air ducts, factory tools, old paint, etc. that cause foaming.

 
6. The influence of some inferior primer and putty. We have learned that there are some extremely low-priced primers and putties on the market, which use excessive fillers to reduce costs. These primers or putties have extremely poor water resistance. When the ambient humidity is too high, they will Causes the absorption of environmental moisture, and then returns to the topcoat to form prickly heat or blistering.

 
7. Improper use of additives. Additives added to topcoats or primers to prevent various problems can seriously impair foam resistance.

 
8. Effects of old paint or previous repairs. Contamination of old paint or previously repaired surfaces can also cause blistering problems. Such as polishing wax, detergent or other materials.

 
9. Wet-grinding polyester putty, after wet-grinding treatment, absorbs or retains moisture in the micropores, which will also cause foaming problems. After water-grinding the putty, it should be dried with compressed air and then allowed to stand for 1 hour at room temperature before spraying the primer.

 
10. The topcoat is sprayed directly without filling and sealing with a primer after the putty or eye filler is ground, so that the air and moisture existing in the microporous defects of the substrate enter into the coating and cause foaming defects. Of course, the scraping technology of putty also sometimes affects the generation of air bubbles. Poor scraping technology will seal a large amount of air in the putty, so it is necessary to master the correct scraping technology of putty.

 
11. Paint before the gas mixed into the paint is released during stirring. Usually, we recommend adding curing agent and diluent to the paint and stirring thoroughly, then let it stand for 5-10 minutes before painting.

 
12. The temperature of the spraying environment is too high, or the air flow is too fast.

 
13. The spraying air pressure is too low or too high, the flash-off time between passes is too short, the temperature rises too quickly after spraying, or the heating source is too close to the paint surface.

 
14. Polyurethane coatings containing isocyanates react with moisture in the air to produce carbon dioxide gas. Therefore, spraying in a high temperature and high humidity environment, using high solid paint thick coating, polyurethane paint is easy to generate air bubbles.

 
Precaution
 
1. For construction in high temperature and high humidity climate conditions, it is necessary to add some (generally no more than 5% of the total) high-boiling point solvent to the topcoat in advance, which can slow down the surface drying speed of the paint film and make the solvent in the coating sufficient. volatilize to avoid excess accumulation of solvent. At the same time, the volatilization intensity is reduced, so that the surface of the coating film will not be rapidly cooled and the difference with the ambient temperature is too large.

 
2. All surfaces must be clean and free of contamination, and no hydrophilic substances are allowed to remain.

 
3. The grinding water needs to be replaced frequently, and all the grinding dirt should be removed. The last wash should be deionized water or distilled water. If using tap water, be sure to wipe and blow dry with a clean cloth, then dry.

 
4. The dried surface cannot be wiped on it by hand.

 
5. Compressed air and topcoat should be clean and free from contamination.

 
6. The primer or topcoat should be sprayed to an appropriate thickness.

 
7. Sufficient drying time should be left between each layer to allow enough time for the solvent in the middle to evaporate.

 
8. The coating must be allowed to dry sufficiently before being exposed to humidity and high temperature.

 
9. For occasions where a large number of painting operations are carried out throughout the year, it is recommended to install an effective freeze dryer. Drain the air compressor tank daily.

 
remedy
 
Puncture the bubble with a needle to determine the depth of the bubble and use a low magnification magnifying glass to find the cause of the bubble. When air bubbles occur between paint layers, the defective area can be sanded off to expose the intact paint layer before repainting. If the defect is serious, or bubbles occur between the primer and the substrate, the paint layer on the substrate should be completely removed, and then repainted. In fact, blistering is a difficult problem to deal with. To some extent, it is more troublesome than biting the bottom, because this problem may still occur after continuous coating for many times. Bubbles are generally destructive defects of the coating. Reprocessing, in most cases, can only be removed, re-surface preparation, putty scraping or primer spraying.

 
Ø Slight blistering and prickly heat can be dealt with by the following methods: Polish with soapy water until smooth, seal with two-component secondary primer, and re-spray with secondary paint after drying.

 
Ø If the damage area is extensive and its depth reaches the primer layer, the paint should be removed to the primer or metal surface and then re-applied.