The influence of weather on painting

There is relatively more rain in the first summer, especially in the rainy season. After every rain, because of the evaporation of water, the air humidity is particularly high, and painting is very easy to turn white, especially nitrocellulose paint. At this time, we should pay attention to the construction. There are two preventive methods: 1, adding a proper amount of waterproof white water (no more than 8% of the total thinner) during paint mixing; 2. Wet the site before painting. Paint bubbles easily in hot weather. Painters generally use less curing agent to avoid foaming. Some people even add 50% of the standard amount! Actually, this is a misunderstanding. Reducing curing agent can't substantially avoid coating foaming, but it will lead to incomplete coating reaction, resulting in soft paint film and poor adhesion. If it is a primer, it is easy to cause undercut, and if it is a high-grade topcoat, it will also cause unstable luster. The main reason why paint bubbles easily in summer is that the surface of paint film dries too fast. Generally, a proper amount of slow-drying water is added to the diluent (generally not more than 10% of the diluent). Even if less curing agent is added, it is recommended that the primer and semi-dull topcoat be no less than 1:0.45, and the glossy topcoat be no less than 1:0.8. Bright topcoat is particularly prone to prickly heat and pinholes in summer. The reason is that after paint spraying, due to the high temperature and rapid evaporation, the paint surface layer quickly forms a film, and the nonvolatile diluent below the surface layer is prevented from infiltrating into the surface layer, forming needle-like holes. The only way to solve this problem is to reduce the surface drying speed of paint. For example, lowering the ambient temperature, using slow-drying thinner and reducing curing agent can only prolong the rising time of paint hardness, but can not prolong its surface drying time, so it can not effectively remove prickly heat. There are many mosquitoes in summer, which easily fall on the surface of paint film during the drying process of paint, causing paint rework. The following points are suggested during rework: 1. Polish it thoroughly. Wax slurry is generally added to the top coat to increase the smoothness of hand feel. If it is not fully polished before repainting, delamination will occur. 2. When polishing, the sandpaper should not be too thick. During the service, we found that many masters used 240 or 320 sandpaper, or even thicker. Too thick sand marks need thicker paint film, which leads to poor transparency and finally makes panels of different colors; In contrast, more than 320 imported sandpaper is used for grinding. Although the sandpaper on the surface is expensive, only a thin layer is needed when the topcoat is actually repainted, which not only saves the paint, but also makes the surface repainting not obvious. Four general factories have thinner in winter and summer, so it is better to use the corresponding thinner in high temperature weather and it is easier to construct.