How We Eliminated Blistering Issues in Powder Coatings: A Practical Case from Metal Manufacturing

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In metal fabrication, powder coatings are among the most widespread surface treatments due to their durability and environmental benefits. However, blistering issues can lead not only to aesthetic defects but also to reduced corrosion resistance. In this article, we share a specific case from practice where we identified the cause of the problem for an automotive supply chain customer and proposed a permanent solution. We will show how minor adjustments in pre-treatment, application, and curing can eliminate this common defect—and save time and costs on recoating.

Blistering in powder coatings: How we identified the problem

In metalworking, the quality of surface treatment is crucial not only for aesthetics but also for protection against corrosion and mechanical damage. In our case, the customer faced recurring blistering in powder coatings on steel components. The issue manifested particularly after curing, when small but visible defects formed on the surface, reducing the durability and lifespan of the products. The first steps involved analyzing the process: we checked drying parameters, coating thickness, and oven conditions. We found that blisters appeared irregularly, suggesting the cause was not in the powder itself but rather in its interaction with the substrate or environmental conditions.

To gain a deeper understanding of the problem, we conducted a series of tests, including microscopic analysis of the defects and adhesion tests. Interestingly, blisters formed predominantly in areas with greater coating thickness or on sharp edges. This led us to suspect insufficient ventilation of moisture or volatile substances during curing. We also checked the storage conditions of the powder and found that ambient humidity could have affected its properties. These clues guided us toward a systematic solution combining adjustments to process parameters and the selection of more suitable raw materials.

Root Cause Analysis: From Moisture to Incorrect Additives

During a detailed analysis, we focused on three main areas: the substrate material, the composition of the powder coating, and the technological application conditions. For the substrate, we found that the steel components were not sufficiently degreased and contained residual moisture, which was released during curing and caused blistering. This issue worsened in winter months when relative air humidity was higher. We also examined the powder composition—specifically the type and quantity of additives used, which can influence reactivity and gas release during curing.

Another factor was the temperature and curing time. Standard procedures assumed curing at 180 °C for 15 minutes, but our measurements showed that some parts of the oven did not heat evenly. This led to some components being under-cured, while others were exposed to excessively high temperatures, which promoted gas formation. The analysis concluded that the problem was not caused by a single factor but by a combination of several process deficiencies that needed to be addressed comprehensively.

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Step-by-step solution: Process and raw material optimization

The first step was improving the substrate pretreatment. We introduced more thorough degreasing and drying of parts before powder application, including monitoring humidity in the environment. The process was supplemented with measuring residual moisture on the steel surface using standard test methods to ensure consistent quality. We also adjusted the powder storage conditions—ensuring it is kept in a dry and temperature-controlled environment to prevent moisture absorption from the air.

In the area of powder coating composition, we focused on selecting additives with lower reactivity and better compatibility with the substrate. We collaborated with the raw material supplier to adjust the formulation, reducing the content of volatile components and optimizing the ratio of binders to fillers. We modified the technological conditions to ensure even curing—implementing temperature control in the oven and extending the curing time to 20 minutes at 170 °C. These changes led to a significant reduction in blistering and improved the overall quality of the coating.

Results and Practical Recommendations

After implementing the changes, we conducted a series of control tests that confirmed the success of the solution. The occurrence of blisters decreased by over 90%, while the coatings demonstrated better adhesion and resistance to mechanical damage. The customer also noted cost savings due to the reduction in defective products and complaints. A key insight was that even seemingly minor process deviations—such as substrate moisture or uneven curing—can have a significant impact on the quality of the final product.

Based on our experience, we recommend that powder coating manufacturers pay increased attention to several areas: regularly check raw material storage conditions, optimize substrate pretreatment, and ensure uniform curing in ovens. Collaboration with chemical raw material suppliers, who can assist in adjusting formulations for specific applications, is also important. Preventing blistering issues requires a systematic approach and thorough control of all production process stages.

Photo: Pawel Czerwinski / Unsplash

The Role of Surface Pretreatment: An Often Overlooked Factor

Blisters in powder coatings often form already during the pretreatment phase, when residues of oils, salts, or dust can become trapped on the metal surface. These contaminants then produce gases during the coating curing process, which attempt to escape and cause characteristic defects. In our case, we found that even with an apparently clean surface, microscopic residues of the phosphating bath remained, which were not sufficiently rinsed off. This problem was particularly evident in parts with complex geometry, where the rinse water did not drain evenly.

The solution involved introducing a control step using indicator tests for residual contamination. We also optimized the flow of rinse water and increased its temperature to 40–50 °C, which improved the solubility of salts. For complex parts, we introduced additional manual rinsing of critical areas. These adjustments reduced the occurrence of blisters by more than 60 % even before changing the coating system itself.

Impact of Storage and Handling of Powder Material

Powder coatings are sensitive to storage conditions, particularly humidity and temperature. In our facility, we found that the powder was often stored near heat sources or in areas with high relative humidity (above 60 %). This led to particle agglomeration and subsequent uneven application, increasing the risk of blister formation. Another issue was the handling of the powder—open containers were exposed to dust and contaminants from the production environment.

To minimize these risks, we have implemented several measures: the powder is now stored in an air-conditioned space at a temperature of 18–22 °C and relative humidity below 50 %. Packaging is immediately sealed in airtight containers with desiccant inserts after opening. We have also introduced regular powder quality checks using a flow test to detect any agglomeration. These steps have contributed to a significant reduction in coating quality variability.

Optimizing Curing Parameters: Temperature and Time as Key Variables

Incorrect curing parameters are among the most common causes of defects in powder coatings. In our case, we found that the standard temperature of 180 °C and a duration of 15 minutes were insufficient for complete curing of coatings on some heavier parts. This led to inadequate venting of volatile components and subsequent blister formation. Conversely, for thin-walled parts, surface overcuring occurred, which impaired adhesion and increased the risk of defects.

The solution was the introduction of a differentiated curing regime based on part weight and thickness. For lightweight parts, we reduced the temperature to 160 °C and the time to 12 minutes, while for heavy parts, we increased the temperature to 200 °C and the time to 20 minutes. We also implemented continuous temperature measurement in the oven using thermocouples to ensure even heat distribution. These adjustments led to the elimination of blisters in 95 % of products and simultaneously reduced energy consumption by 12 %.

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