Many spray painting enthusiasts have encountered this problem: the freshly sprayed paint film suddenly turns white, losing its original gloss and texture. This is the common "whitening phenomenon." Actually, this problem isn't due to poor paint quality, but rather has a clear underlying cause. Today, let's discuss it in detail to help you understand and avoid it.

1. Understanding the Core Principle of Whitening

Simply put, the essence of whitening is "moisture interference": After spraying, the solvent inside the paint film evaporates rapidly. This process takes away a lot of heat, causing the paint surface temperature to drop sharply. At this time, moisture in the air condenses into small water droplets due to the low paint surface temperature. These water droplets sink into the not-fully-dried paint film, causing the resin in the paint film to precipitate, ultimately forming the white, hazy marks we see. Understanding this principle makes finding the specific cause much easier.

2. Five Core Causes

2.1 Excessive Ambient Humidity

This is one of the most common causes. If the humidity in the painting workshop is too high, there will be a lot of water vapor floating in the air. Once the paint surface temperature drops, this water vapor will immediately condense on the paint surface, directly inducing whitening. This is especially important to prevent during the rainy season and in coastal areas.

2.2 Abnormal Ambient Temperature

Temperature issues can cause whitening in two ways: First, if the ambient temperature is too low, or even lower than room temperature, the temperature of the workpiece being painted will drop even further when the paint solvent evaporates, making it easier for water vapor to condense. Second, if the ambient temperature is too high, the warm air can hold more moisture, and once the paint surface cools down, the amount of water vapor released will be even greater, increasing the risk of whitening.

2.3 Poor Selection/Incorrect Use of Thinner

Thinner is key to regulating the fluidity of the paint; choosing the wrong one or using the wrong one can easily cause problems. For example, using a poor-quality thinner or blindly choosing a thinner with a too-fast drying speed will cause the solvent to evaporate rapidly within the paint film. A faster evaporation rate leads to a more drastic drop in paint surface temperature, which in turn attracts moisture from the air to condense, causing whitening.

2.4 Improper Spray Gun/Drying Operation

Neglect in the operational process can also cause problems. For example, setting the air pressure of the spray gun too high will forcibly accelerate the evaporation rate of the solvent on the paint film surface; some people also have the habit of "sweeping dry" the freshly sprayed, damp paint film with the spray gun, which will cause the solvent to evaporate even faster, the temperature to drop sharply, and directly induce moisture condensation on the paint surface.

2.5 Poor Ventilation in the Spraying Area

If the air circulation in the spraying workshop is poor, the water vapor generated during solvent evaporation and the existing moisture in the workshop cannot be discharged in time and will accumulate in the spraying environment. High concentrations of moisture will significantly increase the probability of condensation on the paint surface, essentially creating a breeding ground for whitening.

3. Summary

The core issue of paint film whitening is actually "rapid solvent evaporation and cooling + moisture condensation." To avoid this, the key is to focus on two points: first, control the spraying environment (stable temperature and humidity, ensure ventilation); second, standardize operation and material selection (choose the right thinner, correctly adjust spray gun parameters). By doing these two things well, you can significantly reduce the probability of whitening. Next time you encounter whitening problems, check these five causes one by one to quickly find a solution!