Milkying (Whitening)

Problem Description:

Milkying, or whitening, refers to the appearance of white, hazy spots on the surface during the drying process of especially water-based paints. This occurs when the paint fails to dry properly, causing significant aesthetic issues. Milkying typically results from moisture trapped beneath the paint or environmental factors such as low temperature and high humidity.

Possible Causes:

• High Humidity: In environments with high humidity, the drying process slows down and water vapor can become trapped on the paint surface, leading to whitening. When humidity exceeds 65%, the chance of whitening can rise up to 50%.
• Low Temperature: If the ambient temperature falls below 18°C during painting, the drying rate of the paint decreases, which may trap moisture underneath and cause whitening.
• Rapid Drying (Excessive Heat): In excessively hot conditions, the paint’s top layer dries too quickly, while underlying layers retain moisture, resulting in whitening. Temperatures above 30°C increase the likelihood of this defect.
• Insufficient Drying Time: Not allowing enough drying time between paint layers can cause the lower layer to remain soft and mix with the upper layer, leading to whitening.

Solutions and Precautions:

• Improve Environmental Conditions: Monitor and control temperature and humidity during painting. Ideal conditions are temperatures between 18–24°C and humidity levels between 45–65%.
• Control Temperature and Humidity: Avoid painting under extreme hot or cold conditions. Maintain temperature at 18–24°C and humidity at 45–65% during application.
• Ensure Smooth Surface: A smooth painting surface promotes faster and more even drying, thereby reducing the risk of whitening.
• Thinner Selection for Solvent-Based Paints and Varnishes: Use high-quality, slower-evaporating thinners to improve drying uniformity.