Wood coating is an important step in finishing both interior and exterior products. A proper coating not only protects the material but also enhances its aesthetic value. However, if the application is not done correctly, the surface often develops defects.
Among the most common issues are blistering, crazing, and sagging. These problems damage the appearance and shorten the service life of the product. Understanding their causes and applying the right solutions will help achieve a durable and beautiful wood coating.
COMMON DEFECTS IN WOOD COATING
Blistering
Blistering occurs when the coating film forms bubbles and gradually separates from the wood surface. The main causes are high moisture content in the wood, applying a new layer before the previous one dries, or curing at excessively high temperatures. The result is a rough, uneven surface that peels easily and degrades quickly.
Crazing
Crazing creates a network of tiny cracks that resemble spider webs on the surface. This defect often occurs when the coating is applied too thickly, when incompatible coating systems are combined, or when curing conditions are uneven. Once cracks appear, moisture can penetrate the wood, reducing durability and causing structural weakness.
Sagging
Sagging appears when the coating sags downward, forming wave-like streaks. The main reason is spraying an overly thick layer, using a mixture that is too thin, or applying with incorrect spraying distance. The outcome is an unattractive and uneven finish, which is often difficult to repair without sanding and recoating
HOW TO FIX DEFECTS IN WOOD COATING
Control wood moisture
Moisture content directly affects coating stability. Before application, check and ensure the wood is dry below 12%. Excessive moisture is the leading cause of blistering and peeling
Apply thin layers
A thick layer of coating often results in crazing or sagging. Instead, apply multiple thin coats, allowing each to dry naturally before recoating. This technique ensures an even, strong, and smooth finish.
Use compatible coating systems
Combining incompatible systems, such as PU directly over NC, leads to poor adhesion and cracks. To avoid this, always select a compatible and consistent coating system suitable for the material and intended use.
Control curing conditions
Temperature and humidity in the coating room must remain stable. Overheating leads to blistering, while uneven curing causes cracks. Curing should be moderate, with proper ventilation to allow solvents to evaporate gradually.
Adjust viscosity and spraying technique
Sagging is often the result of low-viscosity mixtures or poor spraying technique. Adjust coating viscosity to the proper level, maintain consistent spraying distance and speed. Equipment must be inspected regularly to ensure stable pressure and spray patterns.
Repair existing surface defects
If defects appear, surface treatment is required before reapplication. For blistering, sand away damaged layers. For crazing, sand the cracked film and recoat with a compatible system. For sagging, sand the sagged area smooth and apply a thinner new layer.
VICHEM – OFFICIAL DISTRIBUTOR OF CERTIFIED CHEMICAL ADDITIVES IN VIETNAM
Vichem is an authorized distributor of chemical additives fully compliant with legal regulations in Vietnam. We not only provide high-quality products but also deliver world-class after-sales services. These include:
- Technical consulting: Supporting customers in selecting the right product for their specific applications.
- Color testing services: Our specialists conduct color-matching trials to ensure results meet design standards.
- Application support: Assisting customers in integrating solutions into their production lines to ensure optimal performance.
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