Electrostatic Powder Spraying - Causes and Solutions for Uneven Coating Thickness. Cause: 1. The rough and bad pre-treatment of workpiece. 2. The curing time is too long or the temperature of curing oven is too high. 3. There are volatile gases in the furnace. 4. The proportion of recycled powder is too large. 5. Two different types of powder mix. 6. Poor quality of powder. Solution: 1. Select the appropriate pretreatment process. 2. Adjust the appropriate curing conditions. 3. Clean the oven. 4. After the recycled powder is filtered, it should be mixed with fresh powder, preferably less than 30%. 5. Thoroughly clean the dusting system before powder change. 6. Replace the good quality powder.