Cleaning and Degreasing before Powder Coating

Lets talk about the first step of the powder coating process: thoroughly cleaning and degreasing. Even if the piece is brand new, it should be cleaned. Powder coat adheres best to clean bare metal. Dirt, oils, and other contaminants left on a powder coated part can cause adhesion issues including complete delamination of the coating, and visual issues such as specks, bumps, of fish eyes visible in the coating.
Following the steps in this article will ensure that your parts are thoroughly cleaned and ready for the next step in the powder coating process.

Powdercoatguide.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.  

STEP 1: Disassemble

The very first step for any part that I powder coat is to disassemble it as much as possible. Remove all fasteners, springs, seals, bearings, electrical components, etc until the part is bare. You cannot thoroughly clean parts that are completely assembled, and you definitely shouldn't powder coat assembled parts. If you are unsure how to disassemble a part, search online using relevant part numbers, model numbers, or descriptions. Chances are there is an article, video, forum that can help you.

Some parts are held together by rivets or pins with no way to remove them. At that point, it is up to you with how much it is worth it to disassemble the part completely. Rivets can be drilled out and replaced with new rivets. Some permanent pins that hold parts together are specialty items and were likely installed using machines that you won't have access to. The same thing with some parts that are pressed together. Most bearings are removable with standard tools or a cheap press however, some parts are pressed together so tightly that they can be considered permanent. With parts like these, it is not realistic to dissemble completely so you will have to make some compromises.

STEP 2: Pressure Wash

The next step of cleaning a part for powder coating is to pressure wash the part. The pressure washer removes a lot of the loose debris like dirt and grease chunks with ease. Pressuring washing can save time and effort by replacing a lot of initial manual scrubbing. I use this Sunjoe Electric Pressure Washer because its output is 1.76 gallons per minute which is the highest I could find in a consumer electric pressure washer. I prefer electric pressure washers for cleaning parts that will be powder coated because many of them are not that big. If you were cleaning a fence or a driveway, a gas-powered pressure washer will save you tons of time over an electric pressure washer, but when it comes to powder coating, generally the parts are much smaller than that, so an electric pressure washer is decent enough and offers more convenience.

With the electric units, I tend to use use the 0° nozzle which is provides the most cleaning action as it focuses all the water into a narrow stream. It only cleans a very small area at a time, but that is the trade-off of using an electric pressure washer. If the part is delicate, such as sheet metal or flat panels, I use the 15° nozzle instead because the 0° nozzle can easily warp the metal. Also keep your hands away from the stream, because the stream will tear up your skin. When cleaning, I run this stream over the entire part until I no longer see the dirt coming off. I wear safety goggles while doing this because it splashes everywhere when hitting something irregularly shaped like a car part.

I do all my cleaning on a patio outside my garage. I use one or two tiers of plastic shelves to set parts on while scrubbing and pressure washing. The soft plastic prevents scratching up the metal on the concrete, it also raises the parts up so I am not bending over to clean everything. The holes in the plastic provide nice drainage during pressure washing and it also allow you to use some reusable zip ties to zip tie smaller parts to the shelves to keep them from being washed away. The reason I like them is that they are modular, you can stack them knee-high or waste-high. You can also lay them all on the ground to do a a set of wheels on, or put two stacks side-by-side for subframes. They are abused and left out in the sun, so I only buy them used or when I see a good deal.



If you are consistently working with larger items or if you are coating professionally, a gas pressure washer or an industrial electric pressure washer would be better choices as they will clean more thoroughly, and the units are more reliable. They are capable of a much higher pressures and can get your parts cleaner before powder coating. They are also capable of doing more damage so avoid really high pressures on sheet metal type parts because it is not very difficult to warp/ruin them.  When choosing a gas-powered pressure washer, I believe the units with Honda GX engines and a CAT pump are the most reliable units available.

If you are a DIY powder coater, it may seem difficult to justify the purchase of a pressure washer just for powder coating. However, owning a pressure washer is useful for cleaning items all throughout a home. However, it is not absolutely required, you can get parts very clean in a sink or outside with a hose using cleaners and scrub brushes. You could even stick your parts in a dishwasher (preferably a spare dishwasher) for some automated cleaning. Pressure washers are very helpful to speed up the cleaning process and they really shine on intricate parts that have a lot of tight corners and crevices.

STEP 3: Soak with Cleaner

Aluminum-Safe Cleaners
After the loose dirt and crud is off, I spray the part down with an aluminum safe cleaner. I am very selective about what I use to clean aluminum. A lot of normal household cleaners can corrode aluminum. After a lot of research on a safe cleaner for aluminum, I decided on Simple Green Extreme: Aircraft and Precision Cleaner. It states all over the bottle that it was formulated specifically for aluminum and precision tools. I checked the MSDS and it is, in fact, not just relabeled simple green. After testing it out, I am very happy with it. Its not too expensive, but online is the only place I could find it. It cleans great. I also tested it by spraying on some scrap cast aluminum pieces I had, and just letting it sit for a couple of days. When I came back to the part and wiped off the cleaner, there was no signs of corrosion at all.

I used Simple Green Extreme on this aluminum cylinder head. Unfortunately, I didn't get a good before picture, but in the picture you can see the area I cleaned compared to area that has not been cleaned yet. 

Cleaning cast aluminum with Simple Green Extreme

Head cleaned with Simple Green Extreme

How to Clean Steel and Iron

Cleaning ferrous metals such as iron or steel is a little more forgiving than cleaning aluminum. You can use the Simple Green Extreme mentioned above with no issues. However, since steel can be cleaned with more readily-available and cheaper cleaners, I save the Simple Green Extreme for aluminum.

For cleaning steel, I use Super Clean, formerly called Castrol Super Clean, which is one of the best all-purpose-cleaners I have ever used. For iron and steel parts, I use it full-strength. I spray it on, let it soak for a couple of minutes, scrub the parts with a brush, and then pressure wash the part clean. Super Clean is corrosive to metals so it must be rinsed completely. Purple Power is another good alternative, but I always find myself using Super Clean over Purple Power.

When cleaning high-strength steel, titanium, or aluminum alloys with chemicals, it is possible to weaken the metal when using acidic chemicals. Most acidic household cleaners use weaker acids so the chances are reduced. However, chemical rust removers and similar products contain phosphoric acid or muriatic acid which can can cause something called hydrogen embrittlement. The non-scientific explanation is that hydrogen atoms from these acids can be absorbed into the metal, affecting the internal structure which can cause the metal to weaken or fail. I always try to avoid using acid-based cleaners on metal parts, in order to avoid hydrogen embrittlement.

STEP 4: Scrub

After spraying down the aluminum part with Simple Green Extreme, or the iron/steel part with Super Clean, I let it soak for about 5 minutes, I spray a little more cleaner on the part and scrub it down with a parts cleaning brush. Tube Brushes are great for scrubbing threaded holes and passages.

A parts washer is a great place to do this task. Its the most convenient place to clean parts, it contains the mess, and constantly sprays recirculated cleaner out of the nozzle. They come complete with a stand or you can get a bench-top model to save some space.

STEP 5: Rinse & Repeat

The next step is to rinse the part off. I use the the pressure washer to with a 15° nozzle for this. Depending on how clean the part is, I may then repeat the scrubbing process and give it a very thorough final rinse with the pressure washer. I then bring the part in the garage and blow it dry with compressed air.



Time Saver: Ultrasonic Cleaner

Another method I use for smaller parts, is an ultrasonic cleaner. I say smaller parts because the larger ultrasonic cleaners can be pretty expensive. They are coming down in price so I am looking into a bigger one. If the part fits in my ultrasonic cleaner, I will use it. Its a great way to reduce some labor. I use the same cleaning solutions inside the ultrasonic cleaner that I mentioned above. Although a very good ultrasonic cleaning solution recipe is 50% vinegar, 50% water, and couple drops of dawn dish soap and some baking soda. This solution will clean steel perfectly down to bare metal. It removes rust, zinc plating, and everything else. However, I still do sandblast all parts before powder coating, regardless of how clean the metal is.


This my ultrasonic cleaner below. It also has a heating function which aids in the cleaning significantly. It works very well for small parts and fasteners. I have cleaned heater cores, throttle bodies, and brake master cylinders, and brake calipers in it also. The great thing about an ultrasonic cleaner is that it can clean where no brush can reach. Sometimes a part looks clean, and then you put it in the ultrasonic cleaner and the water will still turn black. You can see the results below.

Ultrasonic cleaner in progress.

Fresh out of the Ultrasonic Cleaner.

STEP 6: Stripping (If necessary)

If the part has previously been painted or powder coated, this is the point where it should be stripped. Chemical strippers will remove all the previous coatings and also can also remove stuck on contaminants that were not removed yet in the cleaning process. For more details on stripping previous coatings, visit Stripping Powder Coat.

STEP 7: Bake / Outgas Part in the Oven

After the cleaning process, I then bake the part in the oven. This not only dries the metal completely from any moisture that may have been remaining, but it also outgasses the part. Cast aluminum and cast iron are porous. Grease, oils, and other impurities can soak into the metal over time. These impurities can also be in the part from the casting process itself. Outgassing the aluminum or iron consists of baking it at a slightly higher temperature and a little bit longer time than your cure schedule.


For example, say a powders cure schedule is 400°F for 10 minutes. I will outgas the aluminum at 425°F for 20 minutes. I do not start the 20 minute timer until the actual aluminum part is 425°F though. I check the temperature with a non-contact infrared thermometer. If you don't know why you should own an infrared thermometer while powder coating, read this article as they are essential for powder coating. For cast metal parts, you can actually see the part smoking in the oven, this smoke is the oils and contaminants being baked out of the metal. If at 20 minutes, the part is still smoking, I will leave it in until the smoking is done and then an extra 5 minutes for good measure. I outgas every part I powder coat just to be thorough, but it is usually okay to only outgas cast parts or parts that have been in salty environments. I don't notice the extra oven use on my electric bill, but a powder coating shop that has large ovens would notice it.


The reason why you outgas a part before powder coating is to prevent it from happening during the curing stage. If those oils are left inside the metal and you powder coat it and put it in the oven to cure, as the heat cures the powder, it also heats up the oils, causing them to expand. This expanding causes them to escape out of the part, leaving a pinholes in your powder coating finish, as seen below.

Outgassing parts in the oven does solve about 90% of the outgassing problems when powder coating. However there are some parts out there that want to outgas no matter how long you bake it before hand. For parts like these,  outgas forgiving primer powder coats need to be applied before any further powder coating.

Conclusion

Following all of the steps in this article, the aluminum calipers shown below went through the following steps in order to be prepared for sandblasting and powder coating:

Calipers before any cleaning or disassembly

• Disassembled
• Pre-washed with a pressure washer
• Soaked in Simple Green Extreme
• Scrubbed inside and out with various brushes
• Rinsed with a pressure washer
• Submerged in an ultrasonic cleaner with Simple Green Extreme for several cycles
• Submerged in an ultrasonic cleaner with clean water
• Blown dry with compressed air
• Submerged in PowderStrip PS-1L for 15 minutes
• Submerged in clean water mixed with TSP
• Rinsed with pressure washer
• Blown dry with compressed air
• Outgassed in an oven at 400°F for 40 minutes

Calipers after cleaning, before stripping

Completely clean bare-metal calipers ready to be sandblasted and powder coated

After the part is clean, degreased, and outgassed, it is ready for media blasting (sand blasting). Leave a comment if you have any questions about this topic. For a thorough explanation of the remaining steps, head over to "How to Prep for Powder Coating".