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Why Does Powder Coating Flake Off?

November 04, 2018

Why Does Powder Coating Flake Off?

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Powder coating is a great way of protecting metal surfaces; it adheres better than most paint, it’s more durable, and it’s more environmentally friendly. You can get a huge range of vibrant colors, and even control the texture of the finish. Sometimes, though, you’ll see it flake off. This can be really disappointing since it really doesn’t look good and it leaves the metal exposed to corrosion.

Why does powder coating flake off? Powder coating often flakes off because of poor surface preparation during the powder coating process. If there are any oils or contaminants on the metal that aren’t cleaned off thoroughly, the powder coating is almost guaranteed to flake off. 

In this article, I’ll explain exactly how this happens, how you can prevent it from happening to your parts, and what else you need to watch out for when powder coating.

Improper Powder Coat Substrate

The substrate is the material that’s being powder coated. For example, steel or aluminum are common candidates for powder coating.

However, some substrates don’t do well with powder coating. For example, some plastics like LDPE and PCL just plain can’t take the heat. Others are so soft that the coating will crack and flake off later.

Another thing that might not work is aluminum that’s been anodized and dyed. Sometimes and inorganic dye will react poorly with the coating and prevent adhesion, resulting in a powder coating that flakes. Aluminum that’s been anodized and dyed will likely take longer to properly prepare for powder coating since a fair bit of the anodized layer will need to be removed through sanding or blasting.

Rust and corrosion is also a major problem. The powder coat won’t stick and will most definitely flake if this isn’t completely removed.  Conversely, it could also flake off if the metal is too smooth and the coating isn’t able to “bite in” to the substrate.

Improper Cleaning

It’s good practice to bead blast or sand blast parts before powder coating. This will help to rough up the surface for better adhesion, take off any kind of corrosion, and remove any grease or grime.

When sandblasting, it’s important to process the part evenly. Any areas that are blasted too lightly or missed entirely will likely be a problem area for flaking. Any areas that are blasted too heavily might give a different surface texture or shape, especially if a very smooth or glossy powder coated surface is desired. It might be that bead blasting would be a better option.

For textured coatings, rougher sandblasting is less of an issue. Even still, this is a process that requires a certain amount of skill to ensure that it’s done thoroughly.

An alternative to sandblasting is to sand the part. This can be tricky, though, for parts that have small inside corners or detailed geometry. Since it’s difficult to reach these areas with sandpaper, this could result in a surface with poor adhesion, where the powder coating will likely flake off.

Cleaning with a solvent will remove any kinds of oils or other contaminants on the part. The powder coating won’t adhere to any surfaces with oil on them, and powder coating is guaranteed to yield poor results if this step is done improperly.

After abrasive cleaning, the part needs to be rinsed off. This is because media blasting and sanding will leave a dust coating on the part that will prevent adhesion. The rinsing media also needs to be very pure, like distilled water. Otherwise, contaminants will be left on the surface.

One common issue is insufficient rinsing. If the distilled water isn’t applied generously enough, the dust particulates might collect along the bottom of the part instead of being washed away. This will almost guarantee to flake later on since the powder coating will adhere to the dust film instead of the metal substrate.

Improper Powder

There are many different kinds of powder coating. Some are made of thermoplastic, some are thermoset plastic. Within these categories, there are many specific types that are more suited for some substrate materials than others. If you use the wrong powder type that doesn’t match the substrate, you’ll likely get flaking.

For example, aluminum can be difficult to adhere to. That means that the powder used for aluminum is often different from that used for steel. There are also different kinds of powder based on application.

For example, parts that will need to be able to flex might need a softer powder. Springs can be powder coated, but the coating could possibly flake off if the spring is put under extreme compression and the coating is too hard and brittle. A slightly softer, more flexible coating may be more appropriate.

Realistic Expectations

At the end of the day, you need to be reasonable with what you expect to get out of a powder coating. It’s absolutely a great way of protecting surfaced and it’s a very durable coating, but it’s also not impervious to wear and tear over time.

For example, powder coats can chip off or flake over time if the area is exposed to impact. One possible scenario is for springs under a car; rocks hitting the spring when driving over a gravel road at high speed will chip off the coating. Eventually, rust can form under the surface of the coating. Once this develops, the coating is no longer able to adhere to the surface of the metal and it will flake off.

UV light can also break down powder coats. It will degrade the coating, making it lose its color and become weak. Once this happens, it can flake or rub off. It’s a good idea to not leave anything powder coated in intense sunlight for very extended periods of time. However, there are some kinds of powder that are more resistant to UV damage than others.

What to Do When Powder Coats Flake

Usually the best approach to repairing damaged coatings to simply redo it. This can be a fair amount of work. Here’s how to do it properly:

Disassemble the component that needs to be recoated if necessary. Sand it down or media blast it until the part surface is totally even and clean of any contaminants. The old powder coating likely won’t need to be completely removed unless there is a major issue with it. Just blast off anything loose.

If you want it to look good cosmetically, it’s a good idea to “feather” the areas that flaked off. Use some sandpaper to work down the edges of where the coating broke off until it’s smooth. This works great if you’re planning on using a non-glossy or textured coating.

For glossy surfaces, you’ll likely see any imperfections, bumps or waves in the substrate. If you want it to be perfect, your best bet is to blast it down to bare metal.

Once the previous coating is dealt with, continue the cleaning process the same way you would the initial coating. Wipe it with solvent, rinse it off, and make sure that it’s thoroughly clean and dry before redoing the coating.

If you don’t want to go through this much effort, you could also simply do a paint touch-up. Sand down the problem area, feather the coating edges, and try etching the bare metal with acid to provide a good grip. Clean with solvent and let dry. They touch up the area with the closest matching paint that suits the substrate material. The fix will likely be visible, but it will be coated and more corrosion resistant. It will likely look better than the flaked-off powder coat.

Related Questions

Does powder coating scratch easily?

Powder coating is generally tough and scratch-resistant when properly applied and cured. It is often much tougher than typical paint coatings, and it can be applied thicker. However, some types of powder coat are more scratch resistant than others. Overall, it can perform better than many other coatings in abrasive applications.

Why is my powder coating chipping easily?

If your powder coating is chipping easily, it’s most likely a problem with improper curing. If the powder didn’t get baked for long enough it will be much weaker. During the baking process, the powdered plastic has time to interlink and do science stuff which gives the coating its famous strength. If the problem persists, try etching the substrate before powder coating. This will ensure a much stronger bond and will help it to resist chipping.

Leave us a comment below on your tips and tricks for a powder coat job that does not chip, flake or cracks from abuse or outdoor weather.

Jonathan Maes

Hi, my name is Jonathan and I've been working in shops for 12 years. I thoroughly enjoy all the metalworking trades - I've worked as a manufacturing engineer, a machinist, a CNC programmer, a foreman and a toolmaker. There are few things I love more than a great project to sink my teeth into!

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