Common problems and solutions in interior wall painting
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Common problems and solutions in interior wall painting 1. Peeling Peeling is one of the common defects of paint coatings; it manifests as the coating peeling off or rolling up in large areas from the wall, often exposing the underlying surface. There are many reasons for peeling. From the perspective of direct causes, they can be summarized as shown in Table 1-1. Table 1-1 Direct Causes of Coating Peeling Direct Causes Content Product Poor adhesion of the product; improper product selection (for example, epoxy products should be used on the smooth surfaces of stainless steel). Substrate The substrate is very porous, such as when putty without adhesive is used; poor pre-treatment of the substrate, with oil or dust present; the wall surface is not dry before coating application; too thick a coating applied in one go. Environment Water leakage or moisture rising from below. The various situations that lead to peeling are analyzed in detail below. (1) Spalling caused by water vapor: The reasons and analysis for spalling caused by water vapor are shown in Table 1-1-1. Table 1-1-1 Analysis of the causes of peeling due to water vapor; Description of the problems: Excessive water in the substrate causes the coating to peel off or roll up in large areas from the wall. Analysis: When a water pipe breaks, water seeps into the coating, causing bubbles to form in the coating near the pipe; in severe cases, this leads to peeling. Causes identified; Preventive measures; Solutions: In cases of peeling caused by environmental factors, the substrate in the peeled area is moist, with water even seeping out continuously. Bubbles are present, and water can be found inside them after they are punctured. It is necessary to locate and shut off the source of water. All the peeled coating must be removed, the substrate needs to be prepared again, and then a qualified putty should be used to level the surface before repainting. Complementary products are also required. (2) Peeling caused by humidity: The reasons for peeling due to humidity are shown in Table 1-1-2. Table 1-1-2 Analysis of the reasons for peeling caused by moisture. Description of the problem: Since the cement-based substrate is porous, if waterproofing is not properly done, large amounts of water can seep into the wall from below, resulting in widespread peeling of the coating layer. Analysis: As the wall lacks waterproofing, water seeps into the bottom part of the wall and then moves upward through capillary action to the middle and lower sections of the wall, causing the coating layer to bulge; in severe cases, this leads to peeling. Reasons for the problem, preventive measures, and solutions: Environment – Peeling of the coating layer usually occurs at corners or joints; proper waterproofing should be applied there. All peeled-off coating material should be removed, and waterproofing should be reapplied along with reapplication of the coating. Associated products. (3) Peeling due to poor adhesion. Analysis of the reasons for peeling due to poor adhesion is shown in Table 1-1-3. Table 1-1-3 Analysis of the reasons for peeling due to poor adhesion. Description of the problem: Poor pre-treatment of the substrate results in weak adhesion of the coating layer, leading to its peeling off the wall. Analysis: The substrate is very smooth, and the coating layer has little mechanical strength; it can be easily peeled off by hand. Reasons for the problem, preventive measures, and solutions: Environment – The coating layer easily peels off. Deficiencies in pre-treatment can be observed in the substrate, such as being too smooth, having oil stains, or dust. Proper pre-treatment is necessary. The coating layer should be removed again, pre-treatment should be redone, and the coating should be reapplied. Associated products. (4) Peeling due to incompatible products. Analysis of the reasons for peeling due to incompatible products is shown in Table 1-1-4. Table 1-1-4 Analysis of the causes of peeling due to incompatible products. Description of the problem: Inadequate selection of compatible products leads to poor adhesion between the coating system and the substrate, resulting in peeling in certain areas. Analysis: When alkyd paint is used on wooden substrates and then latex paint is applied, compatibility issues arise, and peeling occurs due to poor adhesion. Reasons for this phenomenon, preventive measures, and solutions: The coating layer remains intact but can easily peel off under external forces; there is a clear boundary between the substrate and the peeled-off coating layer. After understanding the characteristics of the substrate, appropriate compatible products should be selected, the existing coating layer should be removed, preprocessing should be carried out again, and new compatible products should be chosen for application. (5) Loose putty: The reasons and analysis for peeling caused by loose putty are shown in Table 1-1-5. Table 1-1-5 Analysis of the causes of peeling due to loose puttyDescription of the problem: Due to the looseness of the putty, even a slightly thick coating can lead to peeling.
Analysis: The use of low-quality putty (for example, putty made solely from gelatin powder) results in no strength or adhesion; as the coating dries and shrinks, it pulls the putty along with it. Initially, this manifests as cracking, followed by peeling.
Cause determination and preventive measures/solutions:
Environment: The coating lacks adhesion; the putty at the bottom turns to powder, and it can be easily removed by gently sanding.
Solution: Use high-quality putty. Remove the existing coating, apply high-quality putty again, and carry out the work anew.
Related products: (6) Excessively thick coating. The reasons for peeling due to an overly thick coating are shown in Table 1-1-6. Table 1-1-6 Analysis of the reasons for peeling caused by excessive coating thickness. Description of the problem: Peeling of the coating occurs due to the use of spraying or scraping methods, or because there is not enough time for the coating to dry. Analysis: When the coating is applied in excessive thickness, the surface dries before the interior does during the drying process; this results in a decrease in the surface’s breathability, while the solvents inside continue to evaporate, leading to problems with the coating. Initially, bubbles form; then these bubbles burst, leading to peeling. Reasons for this phenomenon, as well as preventive and corrective measures: In cases where the coating has peeled off over a large area, some solvent remains on the underlying substrate at the initial stage of peeling. The thickness of the peeled-off coating layer is very large, usually exceeding 500µm. It is necessary to control the thickness of the coating layer, remove the coating again, treat the substrate properly, and apply the coating anew using appropriate products. 2. Cracking is one of the common defects in coatings. It manifests as irregular cracks in the coating, with varying depths; these cracks can take the form of network-like cracks, fine cracks, tear marks, or large cracks. There are many reasons for the cracking of coating films; if we look at the direct causes, they can be summarized as shown in Table 2-1. Table 2-1 Direct causes of coating cracking. Direct causes: Poor weather resistance of the product’s exterior coating; improper selection of the product (e.g., using low-quality products for gypsum boards). Substrate: The substrate is very porous, such as when putty without adhesive is used; the substrate itself cracks. Application: Too thick a layer of coating is applied in one application. Environment: Humidity above 90%, strong winds, and temperatures below 5ºC or even lower. The various situations that lead to cracking are analyzed in detail below. (1) Cracking caused by environmental factors The causes of cracking due to environmental factors are shown in Table 2-1-1.
Table 2-1-1 Analysis of the causes of cracking due to environmental factors
Description of the problem: Cracks appear on the coating in a pattern similar to that on a turtle shell, and these cracks are irregular in shape.
Analysis: The cracks occur because the temperature during application is below the product’s minimum film-forming temperature, or because the wind speed is too high at the time of application, resulting in cracked surfaces that peel off in patches.
Reasons for the problem: …
Preventive measures: …
Solutions: …
Environmental factors: Severe cracking of the coating; little adhesion between the coating and the substrate, making it easy for the coating to peel off; the coating is brittle. Do not carry out application under conditions that are not suitable. Remove all the cracked coating and apply it again in an environment suitable for application. Use appropriate supplementary products.
(2) Cracking caused by an excessive thickness of the coating
The reasons for cracking caused by an excessive thickness of the coating are shown in Table 2-1-2. Table 2-1-2 Analysis of the causes of cracking due to excessive film thickness. Description of the problem: Cracks or large fissures appear in the film. Analysis: Cracks form in the film when the temperature during application is below the product’s minimum film-forming temperature, or when there is high wind speed during application, resulting in the film peeling off in patches. Reason for judgment: Preventive measures: Solutions: When the applied film has cracks, its thickness is very high, usually exceeding 500µm. It is necessary to control the thickness of the film applied; all cracked sections should be removed and the application should be repeated under suitable conditions. Associated products: (3) Cracking caused by poor weather resistance of the film. The reasons for cracking due to poor weather resistance of the film are shown in Table 2-1-3. Table 2-1-3 Reasons for Cracking Due to Poor Coating Weather Resistance: Description of the problems includes the appearance of crack patterns on the coating similar to those on a turtle shell. Analysis shows that these cracks occur after the exterior wall coating has been in place for some time, as a result of natural aging, with the condition worsening over time. Reason assessment, preventive measures, and solutions: The coating develops cracks after undergoing a period of aging; it appears old and may even be covered with algae. The coating still has adhesion to the substrate, but dusting occurs when touched. Use products with good weather resistance, remove all the existing coating, carry out proper substrate preparation, and then apply new coatings using suitable products. (4) Cracking caused by high moisture levels in the substrate: The reasons for cracking due to high moisture levels in the substrate are shown in Table 2-1-4. Table 2-1-4 Analysis of the causes of cracking due to high moisture in the substrate Description of the problem: Excess moisture in the substrate leads to the appearance of uniform crack patterns on the painted surface after it dries. Analysis: If the putty has not dried or if there isn’t enough time for a second coating, the substrate retains a high level of moisture, resulting in crack patterns on the surface of the paint; moreover, the higher the moisture content in the substrate, the more severe the cracking becomes. A loose substrate can also lead to excessive water absorption; a slightly too-thick coating layer can cause cracking. Reasons, diagnosis, prevention methods, and solutions: Use a blade to scrape off the coating layer from the substrate – some putty will usually be attached to it. Measuring the humidity with a hygrometer will reveal that the humidity level is high. Pay attention to the construction requirements and ensure sufficient drying time. Remove all coating layers and putty, then apply putty again. Use properly matched products for the work. (5) Wall cracking: The reasons for wall cracking are shown in Table 2-1-5. Table 2-1-5 Analysis of the causes of wall cracking: Description of defects – Large cracks appear in the coating, often at window sills, corners, and areas where items are hung. Analysis: Cracks occur in the wall due to displacement, which in turn causes the putty and coating to crack as well. Causes: Prevention measures and solutions: If the substrate has large cracks that allow visibility into the interior of the wall, and if the coating can be scraped away to reveal cracks in the wall, it is necessary to pay attention to the construction requirements and ensure sufficient drying time. The cracked parts of the coating should be removed and re-applied. It is advisable to use products designed to resist cracking. (6) Substrate cracking: The reasons for substrate cracking are shown in Table 2-1-6. Table 2-1-6 Analysis of the causes of substrate cracking: Description of the defect – Capillary cracks resembling hair strands or tree roots appear on the coating (with a crack width of approximately 0.08 mm), but in small numbers. Analysis: Capillary cracks in the wall or plaster layer cause the topcoat to crack as well; the depth of these cracks is related to the cause behind them. If the cracks are in the wall itself, they are usually deep; whereas the cracks in the substrate are generally shallower. Reasons, prevention methods, and solutions: Scrape off the coating and putty layer using a blade. If the cracks appear in the wall, it’s a wall-related issue; if they appear in the putty, it’s a putty-related problem. Prevention is difficult. Remove the cracked coating section and redo the application. For compatible products, choose those that are resistant to cracking
Description of the problem: Cracks appear on the coating in a pattern similar to that on a turtle shell, and these cracks are irregular in shape.
Analysis: The cracks occur because the temperature during application is below the product’s minimum film-forming temperature, or because the wind speed is too high at the time of application, resulting in cracked surfaces that peel off in patches.
Reasons for the problem: …
Preventive measures: …
Solutions: …
Environmental factors: Severe cracking of the coating; little adhesion between the coating and the substrate, making it easy for the coating to peel off; the coating is brittle. Do not carry out application under conditions that are not suitable. Remove all the cracked coating and apply it again in an environment suitable for application. Use appropriate supplementary products.
(2) Cracking caused by an excessive thickness of the coating
The reasons for cracking caused by an excessive thickness of the coating are shown in Table 2-1-2. Table 2-1-2 Analysis of the causes of cracking due to excessive film thickness. Description of the problem: Cracks or large fissures appear in the film. Analysis: Cracks form in the film when the temperature during application is below the product’s minimum film-forming temperature, or when there is high wind speed during application, resulting in the film peeling off in patches. Reason for judgment: Preventive measures: Solutions: When the applied film has cracks, its thickness is very high, usually exceeding 500µm. It is necessary to control the thickness of the film applied; all cracked sections should be removed and the application should be repeated under suitable conditions. Associated products: (3) Cracking caused by poor weather resistance of the film. The reasons for cracking due to poor weather resistance of the film are shown in Table 2-1-3. Table 2-1-3 Reasons for Cracking Due to Poor Coating Weather Resistance: Description of the problems includes the appearance of crack patterns on the coating similar to those on a turtle shell. Analysis shows that these cracks occur after the exterior wall coating has been in place for some time, as a result of natural aging, with the condition worsening over time. Reason assessment, preventive measures, and solutions: The coating develops cracks after undergoing a period of aging; it appears old and may even be covered with algae. The coating still has adhesion to the substrate, but dusting occurs when touched. Use products with good weather resistance, remove all the existing coating, carry out proper substrate preparation, and then apply new coatings using suitable products. (4) Cracking caused by high moisture levels in the substrate: The reasons for cracking due to high moisture levels in the substrate are shown in Table 2-1-4. Table 2-1-4 Analysis of the causes of cracking due to high moisture in the substrate Description of the problem: Excess moisture in the substrate leads to the appearance of uniform crack patterns on the painted surface after it dries. Analysis: If the putty has not dried or if there isn’t enough time for a second coating, the substrate retains a high level of moisture, resulting in crack patterns on the surface of the paint; moreover, the higher the moisture content in the substrate, the more severe the cracking becomes. A loose substrate can also lead to excessive water absorption; a slightly too-thick coating layer can cause cracking. Reasons, diagnosis, prevention methods, and solutions: Use a blade to scrape off the coating layer from the substrate – some putty will usually be attached to it. Measuring the humidity with a hygrometer will reveal that the humidity level is high. Pay attention to the construction requirements and ensure sufficient drying time. Remove all coating layers and putty, then apply putty again. Use properly matched products for the work. (5) Wall cracking: The reasons for wall cracking are shown in Table 2-1-5. Table 2-1-5 Analysis of the causes of wall cracking: Description of defects – Large cracks appear in the coating, often at window sills, corners, and areas where items are hung. Analysis: Cracks occur in the wall due to displacement, which in turn causes the putty and coating to crack as well. Causes: Prevention measures and solutions: If the substrate has large cracks that allow visibility into the interior of the wall, and if the coating can be scraped away to reveal cracks in the wall, it is necessary to pay attention to the construction requirements and ensure sufficient drying time. The cracked parts of the coating should be removed and re-applied. It is advisable to use products designed to resist cracking. (6) Substrate cracking: The reasons for substrate cracking are shown in Table 2-1-6. Table 2-1-6 Analysis of the causes of substrate cracking: Description of the defect – Capillary cracks resembling hair strands or tree roots appear on the coating (with a crack width of approximately 0.08 mm), but in small numbers. Analysis: Capillary cracks in the wall or plaster layer cause the topcoat to crack as well; the depth of these cracks is related to the cause behind them. If the cracks are in the wall itself, they are usually deep; whereas the cracks in the substrate are generally shallower. Reasons, prevention methods, and solutions: Scrape off the coating and putty layer using a blade. If the cracks appear in the wall, it’s a wall-related issue; if they appear in the putty, it’s a putty-related problem. Prevention is difficult. Remove the cracked coating section and redo the application. For compatible products, choose those that are resistant to cracking
(7) Cracking caused by wet substrate The reasons for cracking due to a wet substrate are shown in Table 2-1-7. Table 2-1-7: Causes of cracking due to moist substrate – Description of the problem: Capillary cracks resembling hair strands or tree roots appear on the coating, but in small numbers. Analysis: Moisture in the wall or putty, or a short time since repainting, results in a slight amount of moisture in the substrate, which causes the topcoat to crack. Reason for cracking: Prevention measures and solutions: Use a blade to scrape off the coating; some putty will usually stick to it. Use a thermometer to check the humidity level, as it is likely to be high. Pay attention to the construction requirements and ensure sufficient drying time. Remove the cracked sections of the coating and redo the application. Related products: (8) Cracking caused by local stress. The reasons for cracking due to local stress are shown in Table 2-1-8. Table 2-1-8 Analysis of the causes of cracking due to local stress. Description of the problem: Irregularities in the substrate generate local stress, which causes cracks in the coating that resemble those caused by tearing fabric; this is common in cases with carved gypsum moldings. Analysis: Capillary cracks in the wall or plaster layer lead to cracking in the topcoat; the depth of these cracks depends on the cause. If the cracking is in the wall itself, it is usually deep; whereas cracks caused by local stress are generally shallower. Reasons for this, along with preventive measures and solutions: Cracks in the substrate appear as tears and mainly occur when the surface of the substrate is uneven. Use flexible coatings or apply thin layers to remove the cracked sections of the coating and then apply it again, along with appropriate complementary products. 3. Bubbling is one of the common defects in coatings; it manifests as the appearance of many bubbles during or after the drying process of the coating. Some of these bubbles form over time, while others are caused during the application process. After the coating dries, some bubbles remain sealed, while others are partially broken. There are many reasons for blistering in the coating film. If we look at the direct causes, they can be summarized as shown in Table 3-1. Table 3-1 Direct Causes of Coating Bubbling. Direct causes: Poor breathability of the product; poor water resistance of the product; poor defoaming properties of the product; poor adhesion of the product. Other factors include damp substrates or walls, applying too thick a layer of coating in one application, insufficient application time, as well as water leakage in the environment or moisture rising from below. The various situations that lead to bubbling are analyzed in detail below. (1) Bubbling caused by poor breathability of the product. The reasons for bubbling resulting from poor breathability of the product are shown in Table 3-1-1. Table 3-1-1 Analysis of the reasons for bubbling caused by poor product breathability. This defect is mainly observed in oily products or water-based products with a high content of emulsions. Due to the poor breathability of the product, and because the matching products were not used. When applying the product to a loose substrate, bubbling occurs during the drying process. High-quality products require specific conditions from the substrate during application; if the substrate is loose and no primer is used, the coating will continue to form bubbles as it dries, and these bubbles are difficult to burst. Reasons for this phenomenon, along with preventive and corrective measures, are as follows: After applying the product to the substrate, there are few bubbles at first, but after a while many bubbles appear from beneath the surface. These bubbles are small, with a size of around 1 mm or less, and they are quite difficult to burst. To address this issue, seal the substrate by applying a primer, sand off the bubbles, and then apply the primer and topcoat again. (2) Bubbling caused by poor water resistance of the product: The reasons for bubbling due to poor water resistance are shown in Table 3-1-2. Table 3-1-2 Analysis of the reasons for bubbling caused by poor water resistance of products. Description of the problem: The product has poor water resistance, and many small bubbles appear in the coating when it is exposed to water. Analysis: After the coating is prepared, part of it gets submerged in water; due to its poor water resistance, water penetrates into the coating, resulting in the formation of many small bubbles over time. Reasons for this phenomenon, preventive measures, and solutions: Bubbling occurs in the coating after it is exposed to water, causing the coating’s quality to deteriorate. It is necessary to use high-quality coatings, remove the defective coating, and apply primer and topcoat again. (3) Bubbling caused by excessive coating thickness: The reasons for bubbling resulting from thick coatings are shown in Table 3-1-3. Table 3-1-3 Analysis of the causes of bubbles due to coating thickness. Description of the problem: When the coating is applied in excessive thickness, bubbles may form in certain areas. Analysis: With the adoption of the new application technique of airless spraying, it is easy to apply a thick layer of coating, which can lead to the formation of bubbles in some areas. Reasons for this phenomenon and preventive measures/Solutions: Control the thickness of the dry film; remove the problematic coating and apply the primer and topcoat again. (4) Bubbling caused by water on the substrate: The reasons for bubbles resulting from water on the substrate are shown in Table 3-1-4. Table 3-1-4: Causes and effects of bubbling due to moisture in the substrate. Moisture in the substrate causes the coating to bubble, and water comes out when these bubbles burst. Analysis: After rain, water seeps into the walls from corners or rooftops, leading to localized bubbling, which gradually disappears once the weather clears. Reason for occurrence: Moisture infiltration or upward migration of underground humidity. Prevention measures: Apply a waterproof coating. If humidity is the cause, it is necessary to locate the source of moisture and cut off its flow. Remove the bubbled areas, redo the surface preparation, and apply the coating again along with related products. (5) Bubbling caused by airless spraying of high-PVC products. The reasons for bubbling resulting from airless spraying of high-PVC products are shown in Table 3-1-5. Table 3-1-5 Analysis of the reasons for bubbling in high-PVC products during airless spraying Description of the problem: A large number of microbubbles are formed in the coating during application, and after drying, numerous pinholes or bumps appear on the coating. Analysis: When high-PVC products are sprayed using airless spraying, a large number of microbubbles emerge from the bottom of the coating; these microbubbles sometimes persist until just before the coating dries. If the coating is thick, this results in the appearance of pinholes after it dries. If these imperfections are polished off before repainting, pinholes will appear after the repainting. Reason for this issue, preventive measures, and solutions: During construction, such imperfections occur; after polishing them, hollow areas are left behind. It is necessary to control the thickness of the coating layer, polish thoroughly, and clean away any remaining primer or topcoat – be careful not to polish too much. 4. Low resistance to dirt: Low resistance to dirt is one of the drawbacks of coatings; it results in the walls becoming contaminated with dirt that cannot be cleaned away. There are many reasons why the coating is not resistant to staining. If we look at the direct causes, they can be summarized as shown in Table 3-4.
Table 4-1 Direct causes of poor stain resistance of coatings. Content: Caused by the product substrate, construction environment, and product structure; stain resistance varies greatly depending on the structure. Little to no impact; there is basically no effect under normal construction conditions, and also in normal environmental conditions. The various situations related to poor stain resistance are analyzed in detail below. (1) Indoor pollutants: Indoor pollutants are listed in Table 4-1-1. Table 4-1-1: Description of the problems caused by indoor pollutants. Indicators such as shoe prints, lipstick marks, and handwriting residues that accidentally end up on walls cannot be removed completely. The reason for this is that water-based products are not dense enough; different designs result in varying levels of resistance to stains. In the case of engineering paints, the loose resin structure allows water-based ink to penetrate easily, making it impossible to remove such stains. Prevention measures and solutions: Test products using ballpoint pens and gel pens to see if the marks can be erased without causing much damage to the coating surface. Choose products with good resistance to stains. (2) Outdoor pollutants: Information on outdoor pollutants is provided in Table 4-1-2. Table 4-1-2 Description of the disadvantages of outdoor pollutants: After being applied for a period of time, exterior wall coatings gradually turn gray and dirty, and this phenomenon is more evident in industrial cities. Analysis shows that pollutants in the air adhere to the exterior wall surface and cannot be removed by rain or strong winds. Reasons for this issue, preventive measures, and solutions: The coating surface appears dirty; water or detergent can remove some of the dirt. It is advisable to choose hydrophilic products with good hydrophilic properties, and manual cleaning of the dirt should be carried out. 5. Poor leveling: Poor leveling is one of the common defects in coatings. It results in traces remaining after application; if the coating’s leveling quality is poor, these traces become very noticeable and unsightly, such as brush marks or roller marks. There are many reasons for poor film leveling. If looking at the direct causes, they can be summarized as outlined in 5-1. Table 5-1 Direct causes of coating leveling defects. Direct causes: Product substrate, construction environment, and product structure. Different structures result in significant variations in their stain resistance; there is basically no impact. Under normal construction conditions, there is basically no impact, and in normal environments as well, there is basically no impact. The various situations related to leveling defects will be analyzed in detail below. (1) Leveling issues caused by construction operations The leveling issues resulting from construction operations are shown in Table 5-1-1. Table 5-1-1 Description of the problems related to leveling caused by construction operations. Irregular construction methods result in visible marks on the surface, leaving no time for proper leveling. Analysis: Uneven application force during brushing, with some areas being brushed more heavily than others, leads to numerous brush marks. Causes and preventive measures/Solutions: The coating layer appears uneven in thickness due to irregular construction; follow the standard procedures for construction. After the first coat dries, sand the surface smooth before applying 1–2 more topcoats. (2) Leveling problems caused by dry substrate. The problems related to leveling caused by a dry substrate are shown in Table 5-1-2. Table 5-1-2: Description of the problems caused by substrate drying leading to uneven coating. Due to extremely dry areas on the substrate, a coating with a strong uneven texture is formed, or the unevenness of the substrate becomes fully apparent. Analysis shows that extreme dryness of the substrate results in uneven application of paint during brushing, severe brush marks, and rapid drying that prevents the coating from leveling out. Reasons for this phenomenon, preventive measures, and solutions: There is significant resistance during substrate treatment, and water can be observed seeping into it; the coating dries very quickly. Prevention is difficult. After the first coat dries, sand it smooth and apply 1–2 more topcoats. (3) Problems related to the dilution ratio: The issues caused by the dilution ratio are shown in Table 5-1-3. Table 5-1-3 Description of the problems caused by high dilution ratios regarding leveling. When the dilution ratio is too low, the paint remains thick, resulting in visible application marks and difficulty in leveling. Analysis: A low dilution ratio leads to high paint viscosity; when rolled on, small patterns are formed but the surface has a strong uneven texture, making it difficult to level, and the application process also encounters greater resistance. Reasons for this phenomenon: High viscosity during application, accumulation of paint at the starting point of application, and a thick coating layer. Solutions: Dilute the paint according to the recommended ratio. After the first coat dries, sand the surface to make it smooth, then dilute the paint according to the normal ratio before applying 1–2 more coats of topcoat. 6. Fading or discoloration: Fading or discoloration is one of the common problems associated with coatings. It occurs when colored paints change color over time, and in most cases, the original color cannot be restored ； Color change refers to the alteration in color of a coating after it has been in use for some time, or the precipitation of substances of different colors on the surface of the coating. There are many reasons for the fading or discoloration of coatings. In terms of the direct causes, they can be summarized as shown in Table 6-1. Table 6-1 Direct Causes of Coating Fading or Discoloration. Direct causes: Poor weather resistance of the pigments used in exterior wall products; poor weather resistance of the exterior wall products themselves; failure to use compatible products; excessive water-soluble substances in the product, which are carried to the surface by water; overly alkaline substrate; large amounts of water-soluble substances in the substrate, which are brought to the surface by water; carrying out further construction before the coating has fully dried; using multiple construction methods simultaneously, with areas where they meet each other; exposure to moisture in the environment, leading to reactions with chemicals. The various situations that cause fading or discoloration are analyzed in detail below. (1) Fading caused by pigments The fading caused by pigments is shown in Table 6-1-1. Table 6-1-1 Description of fading defects caused by pigments: Due to the poor weather resistance of certain pigments, the color of coatings fades after a short period of time when exposed to indoor or outdoor conditions. Pigments with good weather resistance do not fade easily when used in coatings, whereas those with poor weather resistance tend to fade more readily, especially organic pigments. Reasons for this phenomenon, preventive measures, and solutions: The product’s color fades, but the coating film does not become powdery; color changes are minimal in areas with less exposure to sunlight. Use pigments with good weather resistance, clean the surface, and apply the coating directly after it dries; use products with excellent weather resistance. (2) Fading caused by poor weather resistance of coatings: Information on fading resulting from poor weather resistance of coatings is shown in Table 6-1-2
Table 6-1-2 Description of the discoloration problem caused by poor weather resistance of coatings. Due to the low weather resistance of pigments, coatings age after being exposed to indoor or outdoor conditions for a short period of time, resulting in a lighter color. Image analysis shows that pigments with poor weather resistance become powdered on their surface after aging, which leads to a lighter color. Reasons for this phenomenon, preventive measures, and solutions: The product’s color lightens, and the coating layer becomes powdered; the degree of color change and powdering is less in areas with less exposure to sunlight. Use pigments with good weather resistance, sand off the powdered coating, and select well-quality complementary products. (3) Color changes caused by soluble substances in the coating layer. Color changes caused by soluble substances in the coating layer are shown in Table 6-1-3. Table 6-1-3 describes the discoloration problems caused by solutes in the coating film. Due to the use of too many water-soluble substances in the formula, these substances seep out under the influence of water, resulting in a poor quality coating film. Analysis shows that the excessive use of water-soluble substances, along with exposure to humid environments such as kitchens or bathrooms, causes these substances to dissolve, migrate, and emerge on the surface of the coating film, thereby deteriorating its quality. Cause determination, preventive measures, and solutions: Spots or streaks on the coating film can be removed by washing with water; avoid using low-quality products, and if possible, clean the surfaces with detergent. (4) Discoloration caused by solutes in the substrate: The discoloration resulting from substrate solutes is shown in Table 6-1-4. Table 6-1-4 Description of discoloration defects caused by solutes in the substrate: After painting is completed, water marks appear after a few months, and initially droplets of water remain on the painted surface. Analysis shows that putty prepared from raw glue powder without any adhesive was used, and no appropriate primer was applied. When water leaks in or moisture from below rises to the surface, the solutes in the putty are brought to the surface, resulting in water marks. Cause, prevention measures, and solutions: Obvious water marks on the substrate may develop mold over time; avoid using low-quality putty, cut off the source of water, thoroughly clean and dry the surface, then apply a sealing primer and topcoat. (5) Discoloration caused by wax precipitation: Discoloration resulting from wax precipitation is shown in Table 6-1-5. Table 6-1-5 Description of discoloration defects caused by wax precipitation. Wax precipitates on the surface of the coating. Analysis: The substrate was treated with wax, and no treatment was carried out before applying the new coating, resulting in the wax being dissolved by the coating and migrating to the surface. Causes, diagnosis, preventive measures, and solutions: Wax precipitation on the product surface – Perform proper pre-treatment, remove the existing coating layer, and carry out proper pre-treatment again before application. Compatible products for use. (6) Discoloration caused by application problems: Discoloration resulting from application problems is shown in Table 6-1-6. Table 6-1-6 Description of discoloration defects caused by construction issues: Using several different construction methods on the same wall surface, or making local adjustments with tools before the coating has dried, can all lead to color changes. It should be noted that colored coatings may change color during the drying process, and the color on the surface is often different from that inside; making local adjustments with tools at such times will cause color changes in those areas. Reasons, preventive measures, and solutions: Color differences at the interface due to construction issues, as well as uneven surface marks from construction – use the same construction method, and redo the work using that same method. 7. Chalking: Chalking is one of the common defects of coatings. It manifests itself as powder sticking to the hands or cloth when wiping the coating, and damage can be observed in the areas that have been wiped. There are many reasons for the flaking of the coating film; if we look at the direct causes, they can be summarized as shown in Table 7-1. Table 7-1 Direct Causes of Paint Flaking. Direct causes: Low-quality products; improper product design; poor weather resistance in exterior wall products; the substrate being extremely porous, for example due to the use of putty that hasn’t been mixed with water; an excessive dilution ratio during application; poor mixing during spraying or fog forming after drying; an environmental humidity level above 90% and a temperature below 5ºC. The various situations leading to paint flaking are analyzed in detail below: (1) Paint flaking caused by issues in the formulation design of interior wall products. The issues related to the formulation design of interior wall products that cause paint flaking are shown in Table 7-1-1. Table 7-1-1 describes the problem of powdering caused by issues in the formulation design of interior wall products. When wiping the coating with hands or a cloth, powder is found on the hands or cloth, and damage can be observed in the areas where the coating has been wiped. Analysis shows that this is due to either excessively low costs for interior wall products or improper design, as well as an excessive amount of pigments and fillers, which results in a lack of adhesion in the coating. Diagnosis: Prevention measures: Solution: Wipe the wall surface 10 times with hands or a wet cloth; powder will remain on the hands or cloth. Avoid using too cheap products. Depending on the degree of powdering, it is usually sufficient to apply 1–2 more coats of high-quality topcoat. (2) Powdering caused by poor weather resistance in exterior wall products: Information regarding powdering caused by poor weather resistance in exterior wall products is provided in Table 7-1-2. Table 7-1-2 Description of the powdering defect caused by poor weather resistance of exterior wall products: When wiping the coating with hands or a cloth, powder is found on the hands or cloth; however, this usually occurs only on the surface. The reason for this is poor weather resistance due to either low costs of the exterior wall products or inadequate design, which leads to the coating deteriorating over time. Wiping with hands or a damp cloth will cause slight powdering, and dirt will also adhere. Reason for this phenomenon, preventive measures, and solutions: When wiping the wall several times with hands or a damp cloth, powder will be found on the hands or cloth, along with dirt. Do not use cheap products to remove the powdered coating; instead, use appropriate primers and high-quality topcoats. (3) Powdering caused by environmental factors – The reasons for powdering due to environmental factors are listed in Table 7-1-3. Table 7-1-3 Description of powdering defects caused by environmental factors: When the coating is applied in harsh environmental conditions, the film formation is poor, resulting in a powdered appearance. Analysis shows that even the best water-based exterior wall products will suffer from poor film formation and a powdered appearance if applied in extremely low or high temperatures; streaks can be observed even when it rains. Causes, diagnosis, preventive measures, and solutions: Harsh working conditions lead to a powdered appearance of the coating, with possible cracking in some areas. It is necessary to follow the specified construction requirements and sand off the powdered coating; construction should be carried out under permissible conditions. Supplementary products. (4) Powdering caused by construction factors: The issues related to powdering due to construction factors are shown in Table 7-1-4.
Table 7-1-4 Description of the powdering defect caused by construction issues: When wiping the coating with hands or a cloth, powder is found on the hands or cloth; however, this usually occurs only on the surface. Analysis shows that this issue arises when the dilution ratio of the interior wall coating is too high during application, or when there is no ventilation during spraying, resulting in slight powdering on the surface of the coating. Usually, wiping the surface with a wet cloth resolves this problem. Cause, judgment, preventive measures, and solutions: During construction, wipe the wall several times with hands or a wet cloth – powder will be detected on the hands or cloth. After the wall dries, wiping the same area again will prevent powdering. It is important to follow the construction guidelines; simply wiping the coating gently with a wet cloth is sufficient. 8. Inadequate covering: Inadequate covering is one of the common defects of coatings. The phenomenon it causes is that after the coating dries, it does not fully cover the substrate, and areas of different colors on the substrate can still be seen, giving a sense of transparency. There are many reasons for poor coating coverage. From a direct perspective, they can be summarized as outlined in points 8-1. Table 8-1 Direct causes of poor film coverage. Direct causes: Low-quality products; improper product design; poor application properties of the product. Substrate: The substrate is too dry, making it impossible to apply paint. Excessive dilution ratio, resulting in a too-thin film. Improper application techniques, leading to uneven film coverage. Environmental factors: The impact of environmental factors is minimal. The various situations resulting in poor coverage will be analyzed in detail below. (1) Poor coverage due to the product’s weak covering power; the details regarding poor coverage caused by the product’s weak covering power are shown in Table 8-1-1. Table 8-1-1: Description of the drawbacks resulting from poor covering power of products. During product design, cost constraints lead to a low covering power. Analysis: Due to this poor covering power, it is not possible to fully cover the substrate, especially in areas where there are color differences on the substrate. Cause determination and preventive measures/solutions: Compare the product by rubbing it on black-and-white grid paper; the covering ability can be seen immediately. Product selection: Choose products with good covering power. Increase the number of application times. (2) Poor covering power caused by application methods: The issues related to poor covering power due to application methods are shown in Table 8-1-2. Table 8-1-2 Description of the disadvantages caused by poor coverage due to construction: Irregular construction methods result in noticeable traces of the construction process, with some areas showing exposure of the underlying surface. Analysis: Inconsistent application force during brushing, with heavier and lighter pressure at different times, leads to numerous brush marks and exposure of the substrate in certain areas. Causes: Prevention measures and solutions: Inconsistent thickness of the coating layer and visible construction traces – follow standard procedures for construction; after drying, sand the surface smoothly before applying 1–2 more coats of topcoat. (3) Poor coverage due to dry substrate: The issues related to poor coverage caused by a dry substrate are shown in Table 8-1-3. Table 8-1-3: Description of the disadvantages caused by poor coverage due to dry substrate. Due to the extremely dry condition of certain areas of the substrate, a coating with a very uneven surface texture is formed, allowing parts of the substrate to be visible. Analysis shows that extreme dryness of the substrate results in uneven application of paint during brushing, leading to severe brush marks and exposure of the underlying substrate. Reasons for this phenomenon, preventive measures, and solutions: There is significant resistance during substrate treatment; water seeps inward, and drying occurs rapidly. It is difficult to prevent this issue. After the first coat dries, the surface should be sanded smooth, after which 1–2 more coats of paint should be applied. (4) Poor coverage resulting from an excessive dilution ratio: The problems caused by an excessive dilution ratio are shown in Table 8-1-4. Table 8-1-4: Description of the disadvantages caused by an excessive dilution ratio. Due to an overly high dilution ratio, the paint becomes too thin, resulting in a low amount of paint applied and uneven coverage. Analysis: A high dilution ratio leads to low viscosity of the paint; as a result, less paint adheres to the tools, and thus less paint is applied. Cause determination: Prevention measures: Solution: During application, low viscosity means that less paint adheres to the tools, leading to less paint being applied, as well as easier dusting off. Dilute the paint according to the recommended ratio, and then apply 1–2 coats of topcoat. 9. Wrinkling: Wrinkling is one of the defects of the paint film. It manifests as uneven wrinkles in certain areas of the paint film during or after drying, and these wrinkles do not disappear. An analysis of the wrinkling defect is shown in Table 9-1. Table 9-1: Causes of coating wrinkling – Description of the problems. During the drying process of the coating, wrinkling occurs due to excessive rapid drying of the coating. Cause identification, preventive measures, and solutions: Product – The impact on the product is minimal. Substrate – If the substrate is very porous, use an appropriate filler. Construction method – It has little relation to the construction method; construct in an environment with low wind speeds or high temperatures. 10. Coating splatter during roller coating – Coating splatter is one of the problems that occur during roller coating. This phenomenon happens when the coating splashes in all directions from the bristles of the roller during the coating process. An analysis of the drawbacks of roller coating splatter is shown in Table 10-1. Table 10-1: Causes and Consequences of Spattering During Roll Coating
During roll coating, spattering occurs due to the poor flowability and adhesion of the paint; the spattered paint often lands on the black cardboard laid on the ground, forming spots.
**Causes** | **Diagnosis** | **Prevention Methods** | **Solutions****
--- | --- | --- | ---
**Product** | Improper combination of thickeners in the paint | Adjust the combination of thickeners | Modify the paint formula
**Substrate** | Generally has no relation to the treatment of the substrate | — | —
**Application Process** | Occurs during roll coating | — | —
**Environment** | Basically has no relation to the environment | — | —
11. **Joint Lines**
Joint lines are one of the defects that occur during paint application. This phenomenon arises from inconsistencies in the application technique or differences in the drying rate of the substrate, resulting in variations in gloss and color when applying the same product, and these variations appear at the boundaries between successive applications. An analysis of the drawbacks of roll coating splatter is shown in Table 11-1.
During roll coating, spattering occurs due to the poor flowability and adhesion of the paint; the spattered paint often lands on the black cardboard laid on the ground, forming spots.
**Causes** | **Diagnosis** | **Prevention Methods** | **Solutions****
--- | --- | --- | ---
**Product** | Improper combination of thickeners in the paint | Adjust the combination of thickeners | Modify the paint formula
**Substrate** | Generally has no relation to the treatment of the substrate | — | —
**Application Process** | Occurs during roll coating | — | —
**Environment** | Basically has no relation to the environment | — | —
11. **Joint Lines**
Joint lines are one of the defects that occur during paint application. This phenomenon arises from inconsistencies in the application technique or differences in the drying rate of the substrate, resulting in variations in gloss and color when applying the same product, and these variations appear at the boundaries between successive applications. An analysis of the drawbacks of roll coating splatter is shown in Table 11-1.
Table 11-1: Causes of joint lines, description of defects. During the application process, when the application time is long or the techniques used are inconsistent, uneven gloss or color appears on both sides of the joints formed after the coating dries. Cause, diagnosis, prevention methods, and solutions: The issue is generally not related to the product itself – Wait until the coating is completely dry, then apply it again using the same technique. Substrate: Inconsistent substrates are mainly due to differences in moisture content; wait until the substrate is completely dry. Application technique: Inconsistent application techniques should be avoided; try to use the same technique every time. Environment: This is generally not related to the environment – 12. Uneven gloss: Uneven gloss is one of the defects associated with coatings; it manifests as uneven gloss after the coating dries, especially when viewed from certain angles. An analysis of the problem of uneven gloss is shown in Table 12-1. Table 12-1 Causes of uneven gloss in coatings. Description of the defect: Uneven gloss in the coating occurs after it dries, due to variations in the porosity of the substrate or inconsistencies in the application method. Cause, diagnosis, preventive measures, and solutions: Product – Poor film-forming properties of the product; adjust the film-forming properties of the product, apply putty again, and then apply a new compatible product. Substrate – Variations in the porosity of the substrate; uneven drying of the substrate with localized areas remaining moist; use putty that is suitable for such conditions. Application – Failure to use a compatible primer; use a compatible primer. Environment – Humidity above 90%, temperature below 5ºC; carry out the application in the required environmental conditions. 13. Runoff: Runoff is one of the defects that can occur during coating application. It results in certain areas of the coating becoming thicker as it dries, giving rise to patterns such as “tear marks” or wrinkles. An analysis of the sagging defect is shown in Table 13-1. Table 13-1: Causes of film sagging. Description of the defect: During application, due to low viscosity of the paint or excessive application thickness, the film flattens out too much during drying, resulting in sagging. Causes, diagnosis, preventive measures, and solutions: Product – The product has poor application tolerance; adjust the thickening system to improve the product’s tolerance. Sand off the deteriorated film and apply the paint again using a yellowing-resistant product. Substrate – The substrate has little impact. Application – Excessive dilution ratio; too thick a layer of paint applied at once; uneven mixing after dilution. Adjust the paint according to the recommended dilution ratio, apply it at the recommended thickness, and mix thoroughly. Environment – The environment has little impact. 14. Yellowing: Yellowing is one of the defects of paint films; it occurs when the film turns yellow after being applied to exterior surfaces over time. An analysis of the yellowing defect is shown in Table 14-1. Table 14-1 Causes of Coating Yellowing Description of the defect: The coating has poor aging resistance, which leads to yellowing under exposure to light (UV). Causes, diagnosis, prevention methods, and solutions: Product: The product is not resistant to yellowing; use yellowing-resistant resins or curing agents. Sand the faded coating clean and apply a yellowing-resistant product again. Substrate: It has little impact on substrate treatment. – There is basically no effect on application. Environment: Yellowing is more likely to occur in areas with stronger UV radiation. 15. Mold growth on the surface: Mold growth on the surface is one of the defects of coatings; it manifests as the appearance of mold spots on the coating during its use. The analysis of surface mold growth is shown in Table 15-1. Table 15-1 Reasons for Mold Growth on Coated Surfaces Description of the problem: After being used for a period of time, the coating develops mold spots or algae due to high environmental humidity. Causes Diagnosis Prevention measures Solutions Product: No antifungal agents have been added to the product, or the amount added is insufficient. Add appropriate antifungal agents to the product. Clean the surface thoroughly using a bactericide, then apply a coating system with antifungal properties. Substrate: The substrate itself is already moldy. Clean the substrate thoroughly using an antifungal agent. Construction process: No impact. Environment: High humidity and moderate temperature. There is no solution other than adding antifungal agents to the coating. -----End----- This post was last edited by sosuch on 2007-12-14 at 20:11