Just sprayed the topcoat, yet the primer wrinkled and blistered like skin? This is a classic "lifting" (intercoat lifting) failure. As a professional industrial coating manufacturer, we show you how to identify solvent polarity conflicts and provide 3 preventive solutions to completely eliminate coating cracking and rework.
At the painting site, the most troublesome accident is undoubtedly "lifting" (substrate attack). It manifests as: after the topcoat is sprayed, the underlying primer suddenly swells, wrinkles, or even detaches from the substrate. This not only affects appearance, but also means the failure of the entire coating system.
As an industrial paint manufacturer, we want to tell you that the core logic behind "bottom biting" is: the solvent of the topcoat "dissolves" the primer.
1. Core reason: Strong solvent met a "weak" primer There is a principle in chemistry called "like dissolves like".
- Strong solvent vs. weak primer: If the topcoat (such as polyurethane or nitrocellulose lacquer) contains strongly polar solvents, while the primer (such as alkyd paint) has poor solvent resistance, the solvents in the topcoat will penetrate into the primer film, causing it to soften and swell.
- Polarity conflict: This phenomenon usually occurs when a "strong-solvent topcoat" is paired with a "weak-solvent primer".
2. Construction timing: Spraying the topcoat before the primer is fully dry
- Question: If the primer is in a "semi-dry, not fully dry" state with internal solvents not yet fully expelled, and topcoat is sprayed at this time, the two solvents mix at the interface, which can very easily cause wrinkling.
- Countermeasure: Strictly adhere to the "recoat interval" time specified by the manufacturer.
3. How to prevent "lifting" (paint pulling up the underlying coat)?
- Principle 1: Hard base, soft top. Ensure that the crosslink density and hardness of the primer are higher than those of the topcoat, or use a primer with stronger solvent resistance (such as epoxy primer).
- Principle 2: Like attracts like. Try to use matching products from the same manufacturer and the same system. Epoxy primer + polyurethane topcoat is a recognized stable combination.
- Principle 3: Apply thin coats in multiple passes. If you are concerned about potential lifting or softening of the underlying layer, the first coat of topcoat can be applied as thin as possible to allow the solvent to evaporate quickly and reduce penetration into the base layer.
4. How to remedy if "lifting" occurs? There is no shortcut. The wrinkled area must be completely scraped off and sanded smooth. After it is completely dry, reapply a compatible primer, then proceed with the topcoat spraying.
Conclusion: "Lifting" is a low-level mistake in construction, but it comes at a high cost. Understanding the polarity compatibility between primer and topcoat, and selecting a scientific matching system, is a mandatory lesson for every professional construction team.