The primary cause of back ionization is either a voltage setting that is too high for a top coat, too thick of a coat, an insufficient ground, or a combination of these. A thick coating will make it more difficult for the incoming charged powder to find the ground, and thus lowering the voltage before applying subsequent coats will be necessary to prevent back ionization.
In an application setting: This means that the powder will not want to stick, or will clump / cluster in certain areas making it difficult or impossible to coat evenly.
Q: How can I prevent uneven powder application?
A: If Back Ionization occurs, the charge must be reset by placing the part back in the oven to dissipate the charge after the dry powder has been removed from the part. The best way to prevent Back Ionization is to adjust your guns KV's setting not higher than what is necessary. Keep an average gun distance of 8-10 inches, if you must move closer the KV's should be lowered to prevent overcharging. Top coats should be started at a lower KV than what the base coat is applied at.
Remember, it's better to start with a lower KV setting and increase if needed.
**Note: Spray guns without an output adjustment may require increasing the distance to the part so the charge can dissipate before reaching the part. This may mean having to increase the flow of powder out of the gun, thus possibly increasing powder waste**