Evaporation

• A good paint job relies on a steady evaporation rate. Evaporation is the process of converting liquid into a gas. Liquid leaving the paint forms the sturdy, final film appearance. However, paint will crack if the evaporation occurs too quickly, such as on a hot, dry day. In contrast, slow evaporation causes paint sagging and dripping, like on a humid or rainy day.
  
  

High Heat Effects

• High heat thickens the paint within the container and on the brush, as it slowly dries the paint particles. A thick paint will not spread evenly on a painted surface, causing lumps and brush streak marks. The polymer particles, or plastics, within the paint cannot adequately attach to one another during a fast drying period. The particles require time for uniform connections, resulting in an even, protective paint coating. Resene recommends that painting should stop during high heat periods of the day, especially if painting a hot surface, like the roof.
  
  

High Humidity Effects

• Humidity is the measure of moisture particles within the surrounding air. High humidity impedes the evaporative process. Liquid residing within the paint cannot convert into a gas since the surrounding air is saturated already. The liquid will remain in the paint, causing a failure of the paint's adhesion to the surface, or sagging. This sagging factor affects thicker paint films more than thinner applications.
  
  

Older Painted Surfaces

• High heat and humidity also affect older painted surfaces. After the cold, winter months turn into warmer, spring days, the home's interior houses excess humidity from the heating season. As a result, the humidity finds its way through the home's walls to the backside of the external siding. This siding is typically exposed wood. The humidity condenses against the wood, saturating the exposed surface. As the sun hits the painted side of the home's exterior, the wood's moisture content is drawn through the wood's interior to the exterior paint's surface. Inevitably, the exterior paint begins cracking and peeling from the moisture infiltrating the paint's adhesion area.
  
  

Ideal Paint Conditions

• An ideal day for painting includes a light breeze. The light breeze helps the evaporative process along. A cloudy day aids the painter by keeping the painting surface cool, avoiding rapid drying that causes cracks. Paint areas that are in the shade if the sun is shining.