Powder coating is a relatively simple process, but it only works if certain factors are in place. The primary factor is that the powder coating should be applied to a new or clean surface. Since there are many different kinds of chemistry used in a variety of powder coatings, not all kinds will respond well with one another. That means you need to consider compatibility before applying a new layer of powder coat on an old one.
The best thing to do is to scrape the old coating off before new powder coating is applied. This can be done by sandblasting the object or by using chemicals to strip the powder coating away. This can be a long process that’s much more costly than buffing out a compromised section of coating, which is why we recommend putting powder coating over powder coating as a last resort.