Poor Adhesion
Poor Adhesion: Between the topcoat and primer, or between the topcoat and aging paint, or between the primer and bare surface.
Causes
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Main cause: Incorrect initial cleaning or other surface preparation. If sanding dust or other dirt has not been completely removed, the topcoat cannot firmly adhere to the primer, leading to poor adhesion.
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Incompatibility between the primer and topcoat or between the primer and the substrate.
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The topcoat is sprayed before the primer has dried.
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Insufficient sanding or lack of sanding altogether makes the surface too smooth.
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Low-quality thinner and its poor solvency.
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Topcoats are applied before the first coat has dried, when painting with more than one color.
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When painting with metallic paint, insufficient evaporation time between two layers or too high viscosity.
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Too long a time gap between applying the primer and topcoat.
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An invisible water film is present on the primer surface before spraying the topcoat:
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The weather is too humid when applying the primer.
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The primer surface is left to dry too long during a damp night.
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Solution
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Remove the existing paint by sanding and repaint.