Tech: DIY Powder Coating
If you’ve ever wrenched on restoring a classic car or a vehicle that’s seen its fair share of East Coast weather, you know exactly what I am referring to when I say rust is your number one enemy. I am in the middle of restoring a ’70s Datsun and learned to powder coat for this car as it will play a major role in making this Datsun look new and keep it that way for many years to come. When performing a car restoration, you will or have come across plenty of parts that are either stained, oxidized, or corroded with rust.
By now, you might be asking yourself, why powder coat when you can spray paint? The answer is quite simple. Spray painting is cheap and easy to apply but powder coating compared to paint is advantageous and more resistant to impact, moisture, chemicals, ultraviolet light, and other extreme weather conditions. In turn, powder coating also reduces the risk of scratches, chipping, abrasions, corrosion, fading, and other wear and tear issues often associated with painting. Plain and simple, it’s stronger and tougher.
What is Powder Coating and How Does it Work?
Powder coating is a type of dry coating, which is applied as a free-flowing, dry powder. The powder used in the process is a mixture of finely ground particles of pigment and resin which is applied electrostatically, then cured under heat. The curing process allows the powder to flow and form a durable, high quality finish superior to any spray paint surface. Powder coating is unique in that it requires two main elements to work: an electrostatic charge, and heat. Powder is applied with an electrostatic spray gun to a part that is grounded. The electrostatic charge causes the powder to be attracted to the metal object to be coated. Without it, the powder will not stick to the intended surfaces.
Preparing the Part
Grease and Oil Removal
The first step of the powder coating process is to thoroughly clean and degrease your item, even if it is brand new. All parts must be free of any oil, dirt, or other contaminants prior to moving on to the powder coating process. Prepping involves the stripping of any existing corrosion or coating, the cleaning and degreasing of the bare metal, and the creation of a surface finish adequate for a powder coat. For parts such as intake manifolds, begin the cleaning process by removing any paint or coatings using a caustic chemical stripper and scrub brush. If any of the parts were coated prior to removal with an OEM powder coating, we recommend using a media blaster to remove material.
After the loose dirt and paint is removed, use denatured alcohol or a paint prep cleaner to remove any remaining wax, polish, grease or dirt. Powder coat is 4 to 10 times thicker than traditional liquid spray paint, therefore we highly advise using high temperature tape designed specifically for the powder coating process to protect critical tolerance areas such as brake caliper piston bores. Silicone plugs can be used to plug threaded holes and or studs. If you’ve ever coated before, you know the inconvenience of having to re-thread coated holes. Preparation is key with powder coating. The cleaner you can get the object before beginning, the better the coating is going to flow and, ultimately, the final product will display fewer imperfections.
Powder Coating Guns
Depending on the type of application gun and your level of expertise, powder coating guns can range in cost from a basic $60 airless setup to a few thousand dollars for a professional setup. If you are new to the world of powder coating, or simply looking to coat only a few items as a hobby, we suggest investing in a more affordable model. While the basic premise of applying powder coat is the same regardless of gun type, there are two types of commonly used application guns that are commonly available in the market known as Corona guns. These types of guns use very high voltages but low current to ionize the air/powder that exits the gun with either negative or positive charge.
Internal Air-Generating Applicator
The first type of Corona application gun has an internal air-generating system to eliminate the need for an air compressor, plus a variable-speed trigger and a quick-change powder cartridge. This non-air compressor type unit is an excellent choice for beginners, inexpensive, and produces a lot of very nice finishes. Our first-hand experience using a non-compressor type unit was powder coating a pair of Subaru WRX valve covers in a gloss black finish. We have to admit that the end results came out looking good in overall appearance. What do you think?
- Excellent choice for beginners
- Quick and easy setup
- Does not require an air compressor
- Plastic cup offers limited powder holding capacity
- Overfilling the cup with powder may cause issues such as leaking from the rear of the cup or difficulty when reinstalling back onto the gun
- Base of the handle is prone to cracking and the locking mechanism is prone to failure.
- Difficult to clean and remove any remaining powder
Compressed Air Applicator
The second type of Corona application gun uses compressed air and is popular with both DIY and experienced powder coaters. This system’s most significant difference from the previously-discussed internal air-generating system is the use of compressed air to transfer powder from the hopper to the tip of the gun. For a number of projects shown throughout the article, we used an Eastwood Dual-Voltage Powder Coating System. Dual-Voltage Powder Coating Guns give you the capability to coat small areas using the low (15kv) setting or coat large areas using the high voltage setting (25kv). Additionally, you’ll need a compressed air source (5-10 PSI) from a portable tank with a regulator or a compressor. When using a compressor type gun, a desiccant air dryer and filter should be employed within the air delivery system to keep contaminants and moisture at bay. The presence of any contaminants can cause poor finish quality or cratered finished film.
- Delivers higher, more consistent, transfer efficiency.
- Two-stage power-supply is designed to deliver optimal voltage for small or large scale projects.
- Easy access powder replacement design makes routine cleaning and maintenance fast and uncomplicated.
- More expensive vs. non-compressed guns.
- Requires access to an airline from a portable regulated air tank or air compressor capable of being regulated down to less than 10 psi.
- Compressor condensation or excess oiling can occur causing powder to clump.
- Improper compressor air pressure regulation can affect the overall finish.
Loading the gun is straight forward. The internal air-generating system unit requires filling the detachable cup with your desired powder while the Eastwood Dual-Voltage Powder unit required screwing the supplied powder container onto the application gun. If you plan on using multiple colors, be sure and remove all traces of the previous powder before switching to a new color to eliminate any chance of cross color contamination. Connect a low pressure air line to the gun. The gun requires .5 or more cfm at 5-10 psi, with 8 psi being ideal. Connect the ground clip to the part you are powder coating. Grounding the part provides a path for static charges to dissipate. Unlike regular paint guns, the application gun creates a fog of charged particles. Maintain approximately 8 inches between the gun tip and part being coated. Depress the activation switch while triggering the gun. Depressing the activation switch energizes the gun, charging the powder. Releasing the switch turns the power off. Be sure to coat deeper crevices and inside corners first to prevent uneven coating. The coated surface will have a dull opaque coating of powder. The key to quality powder coating is to spray just the right amount of powder with the minimum amount of air necessary to cover the base material.
During the cure process the powder gradually melts, changing from a dull flat finish to a smooth gloss finish. To cure the powder, use an electric oven or toaster oven large enough to fit the parts but do not use an oven used for food preparation or located in a sealed-off area as mildly toxic fumes are emitted into the atmosphere from the powder while curing. Never use a gas oven as all powder is combustible. For smaller parts we purchased a dedicated electric toaster oven to cure a parts but if they are too big for the oven, consider using an infrared heat lamp. When it came to curing our intake manifold, we built a metal box enclosure along with some tin foil to allow consistent heat dispersal to direct around the manifold. Due to the intake manifold’s size, we cured the unit in two sections starting from front to back.
After becoming a liquid form but prior to curing the parts, be sure to preheat the oven to the powder manufacturer’s recommended cure temperature – most powders will melt and cure at 400 degrees Fahrenheit. Coating porous materials such as cast iron, die cast and cast aluminum, and pot metal parts, trap contaminants. When heated, these contaminants will outgas and cause porosity problems when the powder is cured. In some cases, contaminants in porous materials will cause pits in the powder. To prevent these issues, bake the parts prior to powder coating and thoroughly clean them to eliminate any unwanted contaminants from ruining the final finish.
Powder coating can be applied to aluminum, steel, cast iron, copper, gold, brass, bronze, nickel, stainless steel, and chrome-plated metals. In the past, powder coating has been done by professionals using highly specialized equipment. These requirements have changed with the introduction of affordable and easy-to-use equipment designed to give the end-user all of the benefits of a professional powder coated finish, without the hassle and time of taking the parts to a shop. With literally thousands of colors, shades and textures to choose from ranging from metallic to candy colors, the possibilities of achieving that perfect finish are only limited to the imagination.