I. Methods for Determining Drying Stages
1. Surface Dry Stage
Finger Touch Method: Gently touch the paint film surface with your finger. If it feels soft but not sticky (no paint adheres), it has reached the surface dry state.
Cotton Ball Blowing Method: Place a cotton ball on the paint film surface. If it can be easily blown away without leaving any cotton fibers, it is surface dry.
2. Through Dry Stage
Finger Pressure Test: Firmly press the paint surface with your fingernail. If there is no significant indentation and the hardness is high (e.g., pencil hardness ≥HB), it is basically through dry.
Cotton Ball Test: After placing a cotton ball for 30 seconds and removing it, if only 1-2 cotton fibers remain and can be easily brushed off, it indicates that the through dry stage is complete.
3. Complete Curing
Blade Scraping Test: After scraping the paint film, if the underlying layer and interior are not sticky, and the surface is smooth after sanding, it is completely cured.
II. Environmental and Construction Factors
1. Temperature and Humidity
Drying is fastest at a temperature of 15-25℃ and humidity of 40%-70%. Low temperature and high humidity will significantly prolong the drying time.
During the rainy season, it is recommended to use a dehumidifier or a heat gun for assistance (maintain a distance of half a meter).
2. Coating Thickness
Applying multiple thin coats (2 minutes interval between each coat) dries faster than a single thick coat.
III. Techniques to Accelerate Drying
Ventilation: A fan accelerates air circulation, doubling the drying efficiency.
Heating Tools: Heat gun or small heater (maintain a safe distance).
IV. Precautions
Avoid contact with water, bumps, or direct sunlight before complete drying, otherwise it may cause the paint surface to crack.
Polyurethane coatings require 7 days for complete curing, and continuous monitoring is necessary during this period.
