Powder Coating FAQ – Can You Powder Coat Over Rust and Mil Scale

A common question that is asked when powder coating is if you can powder coat over rust and mill scale. After all, removing rust and mil scale requires an extra step, whether it be removing the rust and mil scale via sandblasting, or by using chemical compounds. This article will answer if you can powder coat over rust and mill scale.

Why You Shouldn’t Powder coat over rust and mil scale

While it is possible to powder coat over rust and mill scale a variety of potential problems can occur, which in general will all lead to your powder coating failing prematurely. When we say powder coating failing we mean a few potential issues have occurred; either rust begins expanding throughout the product surface or the coating itself no longer adheres to the product surface. Knowing what powder coating failure is, we can turn to why powder coating over rust and mill scale is not a good practice. The problem is, if you try to powder coat over rust or mil scale, the underlying rust is still in place. Rust creates two problems, first it limits the ability of your powder coating to bond to the surface of the product, and second, it can creep through your powder coat to the surface. Both these issues, poor powder bonding, or rust working its way through the surface will result in your product wearing in a shorter period of time. If you are only worried about protection for a very limited time and do not have any concern over rust showing up quickly, then you may be able to powder coat over rust or mill scale.

What to do about Rust and Mil Scale when Powder Coating

There are two primary ways you can address rust and mill scale prior to powder coating, chemical removal or sandblasting. For any high volume work, it is typically quicker and more cost efficient to sandblast the rust or mill scale off of the product service. For small occasional work, chemical removal can work well.