Automotive painting requires a delicate balance of temperature and humidity to be successful. Some areas of the country may have limited time spans when painting is advisable. The milky surface produced when the environment is not quite right for painting is called "blooming." Methods to prevent blooming include adding chemical thinners and retarders to the paint. The best way is to just wait for the ideal day.
Work In Dry Temperatures
Automotive paint shops use temperature controlled booths to prevent blooming. At home projects don't usually have the option of a paint booth but some shops may rent them for do-it-yourself projects. According to information provided in Painting and Coatings Magazine by Ing. Toine Dinnissen, a technical specialist with Dow Chemical Company,a relative humidity of 75 per cent at 50 degrees (-12.2 degrees C C) or 85 per cent at 16.1 degrees C (-6.11 degrees C C) should not be exceeded. Because controlling the temperature and humidity is a problem without a booth, paint during a dry, warm day. solvents in automotive paint evaporate more quickly in dry summer weather and prevent the milky, cloudy effect of blooming.
Use Paint Thinners
Thinners and retarders can be used to slow the drying time and allowing the proper evaporation of the paint solvents. These products must be chosen by reading the label and using the one that fits the particular environment. The label should provide the temperature range in which the product works best. Check temperature and humidity with a local weather authority to make sure it matches the recommendations on the label the day the paint job takes place and for the days following to allow for curing time.
Change the Temperature
Change the temperature of the paint and the room the spraying takes place in during time periods when humidity and temperature ride the border of "blooming" issues. Air conditioners and dehumidifiers will help remove humidity---keep a temperature gauge with an additional humidity reading in the space at all times to keep track of both.
Raise the temperature of the thinner and the paint before using---bring the products inside a heated area and allow them to warm up to room temperature. Raising the temperature of the car or area being painted warms the paint surface. A portable forced heat fan in the work area can help raise the temperature.