Pretreating the substrate before applying powder to it is important. At the very least the parts to be coated should be cleaned and have any dirt or oil etc. removed from them. If this is not done then you are going to get powder coated dirt, oil and grease and this will not only affect how the powder performs but also how the substrate performs beneath the powder.
For certain applications such as architectural applications, then a complete pretreatment program is recommended to add an additional protective barrier to the substrate. This will help both the powder and the substrate perform better. It helps clean the substrate and protect against rust or substrate degradation.
During this type of pretreatment process the parts are cleaned using water of a specific PH level. Then the chemical pretreatment is applied. With powder coatings a chrome based pretreatment or a non-chrome pretreatment can be used. Once the pretreatment chemicals have been applied, the parts are rinsed and then sent through a blast oven which quickly dries them off so they are ready to be powder coated.
With powder coatings, there is no primer - chrome based or otherwise - required after the pretreatment of aluminum. This is a huge advantage over liquid coatings as it is one less layer of paint, process, energy and time.
When coating steel, often one of the key considerations is corrosion. After a similar pretreatment process, a primer may be applied. Zinc rich powder primers help add a protective layer that will help guard against corrosion. The powder top coat can then be applied.