• Not triggering the gun at each stroke
• Gun stroked at wrong angle to surface
• Stroking too far from surface
•  Wrong air cap or fluid tip
• Depositing a film of irregular thickness
• Too much air pressure
• Fluid pressure too high
  

Prevention

• Make it a habit to release the trigger after every stroke
• Keep gun at right angle (perpendicular) to surface during stroke
• Maintain 15-25 cm (conventional) or 35 -45 cm (airless) distance to surface
• Ascertain and use correct set up
• Learn to calculate the depth of wet film of finish and develop control
• Use the least amount of air pressure necessary
• Reduce pressure. If pressure keeps climbing, clean regulator on pressure tank.