A Guide to Powder Coating Over an Existing Coating
The very short answer is that yes you can often times apply powder coating over an existing paint. However, prior to doing so there are a lot of important factors to consider. In this article we will cover why you may want to powder coat without removing an existing coating, what you need to consider before powder coating over an existing coating, and how you can powder coat over the existing coating.
Why You Want to Powder Coat over an Existing Coating
One of the greatest benefits to powder coating is its durability as a finish which is one reason why you may want to powder coat over an existing coating. A second reason you may want to not remove the existing coating is that you want to achieve a durable finish with as little added cost as possible. Both of these reasons are good reasons to consider powder coating over an existing coating. However, before choosing powder coating you have to consider the benefits to powder coating, the drawbacks to powder coating, and the potential drawbacks of powder coating without removing the existing coating. To better understand the benefits and drawbacks to powder coating as a process you can read this guide here.
What you Need to Consider before Powder Coating Over an Existing Coating
- To be able to apply a powder coating over an existing coating the underlying coating has to be able to tolerate high temperatures – Typically powder coatings are cured at 250- 400 degrees Fahrenheit and so the underlying coating and part itself must be able to tolerate a high temperature so that the powder can be cured
- You are looking to completely recoat the product – Due to the way powder coating works you are not really able to touch up spots on the product but rather will need to recoat the entire product to use powder coating as a method
- You are ok with a thick film build – Powder coating will typically have a minimum of a 2 mil build but for performance it is more common to have a 6 – 10 mil build on the products surface
- There is no surface rust breaking through the underlying coating – Similar to liquid coatings, powder coating should be applied to a rust free substrate.
- The paint finish is in good shape – The paint applied to the product needs to be free from bare spots in the surface and exhibit good adhesion if the paint is chipping or bare spots are prevalent you should not powder coat over the coating.
- The underlying coating is not excessively thick – If the existing coating is more than 3 – 4 mils thick you may have trouble getting the product to be grounded to effectively use a powder coating gun because it relies on electrostatic principals to apply powder to the product’s surface, you may have to create a bare metal point on the part to be able to ground the part.
- You May Not Get the Same Durability of Finish Compared to Stripping or sandblasting the Product -Much like applying a liquid coating the quality of your surface preparation will determine to a large degree the adhesion of your coating which also determines the durability of the coating. If you do not remove all the coating and create a surface profile on the product but rather create a profile over the existing coating your powder coat may not last as long as you will be more dependent on the bond formed between the original coating and the product surface.
- A powder Manufacturer may not guarantee adhesion specs – If you coat over an existing coating the powder coating manufacturer may not stand behind the performance of their powder, this will be something to check with the powder manufacturer prior to coating over an existing coating.
How you Can Powder Coat over an Existing Coating
Step 1 – The first step to powder coat over an existing coating is to visually check the coating to make sure the underlying coating does not have bare patches, issues with significant peeling off, or rust break through
Step 2- If these issues are not present you should roughen the surface through sanding. If they are present you will need to prep the surface by stripping the old coating.
Step 3 – Clean the product surface – As with any coating application you should clean the surface with an appropriate cleaner to ensure there is no dirt or other surface contaminants present prior to applying the new powder coating.
Step 4- Select the proper settings with your powder coating equipment – To apply powder over an existing paint you will often have to adjust the setting on the powder coating equipment (commonly using a lower KV setting than the typical KV setting used on a new product surface). Often times the powder gun will have a rework settings selector or if not KV settings between 20 – 50 KV’s should be used. Additionally, you may have to increase the amount of powder you are using because you need to ensure the surface is thoroughly covered with powder coating so that you do not get a poor appearing finish.
Step 5 – Cure the powder using the manufacturers recommended cure schedule
While it is possible to powder coat over an existing coating for best results it is usually better to strip any existing coating off the product surface prior to applying an additional coating. If you are frequently recoating products and want to evaluate issues with your painting process contact us today for a free evaluation.