Why does my UV resin cure unevenly?
Light Penetration and Thickness
UV resin cures only where ultraviolet light reaches it. If you pour a thick layer, the top cures while the bottom stays sticky because the light can't penetrate deeply. Most UV resins cure best in layers of 1/8 inch (3 mm) or less, though this varies by brand and resin type.
The color and opacity of your resin also matter. Clear resin lets light through, but opaque or heavily pigmented resin blocks UV, so it may need longer exposure or thinner layers.
- Pour in thin layers, typically no more than 1/8 inch per pass.
- Use a UV lamp with the recommended wavelength (often 365 nm or 395 nm).
- Keep the light close to the resin, following the manufacturer's distance guide.
- Rotate the piece or use multiple lights for complex shapes.
Mold and Surface Factors
Silicone molds can block some UV light, especially if they are thick or opaque. If you're curing inside a mold, the bottom may not get enough light. You can flip the piece or use a transparent mold.
Also, make sure your working area is free of shadows. Even a small object can cast a shadow that leaves uncured spots.
- Use clear silicone molds when possible.
- Cure from multiple angles or flip the piece halfway through.
- Avoid placing the light too far away; follow the lamp's instructions.
Common mistakes
- Assuming all UV resins cure at the same speed and thickness; always check the manufacturer's guidelines.
- Using a weak or old UV lamp that no longer emits enough light to cure properly.
- Pouring too thick a layer and expecting the light to penetrate all the way through.
