Can I powder coat more than a single layer on the same sheet of mild steel? W.F.
Yes you can apply multiple coats, as long as each coat is applied to three mils thickness or less. Thicker coats can be problematic, since the product ground becomes compromised. This can lead to more orange peel, KV starring and other surface defects. Each coat must be continuous (no dust coats) to ensure a smooth finish. You must also consider the over bake resistance for the particular powder coating you are applying and try to compensate each cure cycle to ensure that the base coat is not over cured (< 100% over bake resistance).
Some popular two-coat processes (using organic coatings) are listed below: