Why does paint blister and peel when recoating? A comprehensive analysis of the issues related to interlayer adhesion and additive imbalance.

Why does blistering and peeling occur after recoating? In automotive repair, industrial equipment refurbishment, secondary painting of wooden furniture, and steel structure maintenance, many construction workers encounter these problems: blistering after recoating, paint film peeling, poor interlayer adhesion, localized bulging, increased pinholes, and paint layer separation. Many people’s first reaction is to think: it’s a problem with the construction technique, inadequate substrate treatment, or poor paint quality. In reality, in many cases, the core factor truly affecting the recoating effect often comes from an “imbalance in the additive system.” In particular: leveling agents, defoamers, and dispersants. If the selection is unreasonable or the amount added is abnormal, it can directly affect the interlayer adhesion. This article will systematically analyze the causes of blistering and peeling during recoating, and provide solutions in industrial coatings. I. What is Interlayer Adhesion After Recoating? Interlayer adhesion refers to the bonding ability between the newly sprayed paint layer and the old paint film. Insufficient interlayer adhesion can easily lead to: blistering, delamination, cracking, and large-scale peeling. This is especially likely to occur in the following scenarios: automotive paint touch-up, industrial equipment refurbishment, secondary application of wood coatings, and maintenance of anti-corrosion paints. II. Why do additives affect recoating results? Many people believe that additives are merely “auxiliary materials.” In fact, in modern coating systems, additives play important roles in: leveling, defoaming, dispersion, wetting, preventing pinholes, and surface tension control. However, more additives are not necessarily better. An imbalanced ratio can actually damage the stability of the paint film. III. Why does excessive leveling agent lead to decreased adhesion? The main functions of leveling agents are: improving the smoothness of the paint film, reducing orange peel, and enhancing gloss. However, if added in excess: the paint film surface becomes too smooth. This leads to: new paint failing to effectively “grasp” the old paint layer. This results in: decreased interlayer adhesion, poor recoating bond, and later cracking and peeling, especially noticeable in high-gloss automotive paints and high-gloss wood coatings. IV. Why does excessive defoamer cause bubbling and blistering? Defoamers are used to eliminate air bubbles generated during application. Under normal circumstances, they improve paint film quality. However, if too much is added: It may form: Micropores, pinholes, and localized voids. When recoating: Solvents in the new paint will seep into the old paint layer through these micropores. This subsequently results in: Blistering, localized bubbling, and paint layer separation. The risk is especially high in thick-film industrial paints. V. What problems does dispersant imbalance cause? Dispersants are primarily responsible for: Ensuring pigments are evenly dispersed in the system. If the dispersion system is unstable: It is prone to: Pigment agglomeration, uneven colorant distribution, and localized stress concentration. This reduces: Overall film adhesion, mechanical properties, and interlayer stability, ultimately affecting recoating adhesion. VI. Why do different manufacturers produce such different results with the same paint? Many users find that: For similar products, some are stable after recoating, some are prone to delamination, and some are prone to blistering. The core difference usually lies in: the balance of the additive system. Truly mature paint manufacturers will systematically balance: resin system, solvent evaporation rate, surface tension, and additive compatibility. This is also one of the core technologies of industrial coatings. VII. Which industries are most prone to recoating problems? 1. Automotive Refinish Paint: Automotive refinish paint has very high requirements for interlayer adhesion. If the undercoat is too slippery or additive migration is severe: it can easily lead to: clear coat delamination, edge lifting, and localized blistering. 2. Industrial Anti-corrosion Refurbishment: After long-term use of industrial equipment: the old paint film has aged. If recoated directly: it can easily lead to: poor adhesion, paint layer separation, and localized peeling, especially common in epoxy systems. 3. Secondary Application of Wood Coatings: Wood surfaces are usually smooth. If recoated directly without sanding: it can easily lead to: undercoat peeling, delamination, and paint film cracking. VIII. How to solve the problems of blistering and peeling during recoating? Solution 1: Strictly Control Additive Additive Amounts. Additives must be precisely controlled according to the formula. They cannot be added arbitrarily based on experience. Especially: leveling agents, defoamers, and wetting agents; excessive use will affect system stability. In modern industrial production, the optimal addition ratio is usually determined through: small-scale testing, compatibility testing, and recoating experiments. Solution 2: Sanding Before Recoating. Sanding is an important step in improving interlayer adhesion. Proper sanding can: increase surface roughness, improve mechanical bonding, and remove surface contaminants. Common methods include: dry sanding, wet sanding, and scouring pad treatment. Different systems require different roughness levels. Solution 3: Use Compatible Additive Systems. Additives from different manufacturers: are not necessarily fully compatible. Random mixing may: cause surface tension conflicts, delamination, pinholes, and decreased adhesion. Therefore, it is recommended to: use products from the same system as much as possible. This is especially important in: automotive paints, UV coatings, and high-gloss wood coatings. IX. How to Optimize Recoating Performance of Modern Industrial Coatings? Currently, high-performance industrial coatings typically focus on optimizing: 1. Interlayer wetting ability: Improving the wetting performance of new paint on old paint. 2. Surface tension balance: Preventing interface separation. 3. Solvent evaporation gradient: Reducing solvent impact on the old paint layer. 4. Additive migration control: Reducing surface additive accumulation problems. X. How to reduce recoating rework rate? For construction companies, recoating failures increase: labor costs, material waste, rework time, and project risks. Therefore, it is recommended to establish standardized construction procedures. These include: fixed sanding standards, fixed recoating intervals, fixed dilution ratios, fixed spray thickness, and fixed ambient temperature and humidity. This can effectively improve construction stability. Conclusion: Problems such as blistering, peeling, and bulging after paint recoating are often essentially related to an imbalance in the additive system and insufficient interlayer adhesion. Whether it’s automotive paint repair, industrial anti-corrosion refurbishment, or secondary application of wood coatings, a high-quality coating system cannot be separated from: a reasonable balance of additives, a stable resin system, scientific application techniques, and proper substrate treatment. Truly mature coating manufacturers often improve the stability of the paint film and its long-term recoating performance through refined additive control, thereby achieving more reliable application results and product quality.