Top Coating Techniques
Text by Huw Evans, images by Tracy Stocker
Although exterior paint and bodywork is often what draws attention to a hot rod or custom, the true extent of craftsmanship can often be found under the skin. The frame, engine, transmission, rear end, suspension and brakes often incorporate very unique touches, whether by choice or necessity. Particularly on 1920s and 1930s era cars, many of these greasy bits are exposed, and so great attention is often paid to making items such as axles, valve covers, air cleaners, bell housings, diff covers and even springs look as clean and presentable as the coachwork and interior. However, whether cleaning or painting, keeping the moving parts clean and protected requires a different approach than the body.
One of the biggest problems faced by hot rods that are driven is the accumulation of volatile materials on various parts of the vehicle’s anatomy. This can range from road salt to mud, tar, oil, grease, anti-freeze and brake, power steering and transmission fluid, as well as heat generated from engine operation. Over time, any combination of these factors can cause all kinds of problems – everything from corroded exhaust headers and stained pipes to tarnished air-cleaners, peeling paint on engine blocks and water pumps. It can even cause more serious issues, like cracked rubber or hoses and even serious sheetmetal rust-through (like battery boxes, inner fenders and firewalls, often caused by seeping battery acid or leaked brake fluid). Think how many “nice” looking hot rods you’ve probably come across, only to find that the engine bay was crusty and corroded, or the suspension hardware tarnished, filthy and worn from lack of maintenance.
As hot rodding has evolved over the decades, more and more attention has been paid to details. The quality of cars being built, either professionally or by enthusiasts at home, is constantly improving, and what was considered acceptable in the early 1970s often isn’t today. Moving and mechanical parts, in particular, come under much more scrutiny, and in order to ensure that they work and function correctly, they need to be maintained and protected.
In lock step with the advancing standards in hot rod construction and appearance, a number of companies have also been offering ever more sophisticated finishing techniques, designed to not only improve the looks of specific parts on our vehicles but also durability. Examples include specially-formulated paints for mechanical parts exposed to dirt, moisture and toxic substances, as well as clear coating and powder coating. The latter in particular has gained increasing acceptance among the hot rodding and car enthusiast community because it is relatively straightforward to apply, requires much less clean up and is more environmentally friendly than painting (particularly important since the Environmental Protection Agency has recently altered the standards and regulations for applying automotive paints to project vehicles).
What Is Powder Coating?
In essence, powder coating is the application of very fine, dry particles of pigment or resin that, via an electrostatic positive charge, are sprayed onto a surface that is negatively charged. This allows the particles to adhere to the surface until the coated object can be placed in an oven for baking. As the temperature increases, the particles fuse together (literally cure) to become a hard, durable shell coating that’s highly resistant to scratching or contamination.
Powdercoating came into widespread use during the late 1960s, and most early applications were in heavy industry and commercial sectors such as aircraft or ship parts that were exposed to extremes of temperature or excessive amounts of salt water. Since then, it has become far more widespread and today is used in everything from kitchen utensils to household furniture and, of course, automotive applications. For hot rodders, powdercoating is becoming a preferred choice for finishing items such as intake manifolds, air cleaners, valve covers, water pumps, engine accessories, exhaust components, suspension parts, frames and differential covers. And while you can still farm out various components of your project to be powder coated professionally, it’s now also possible to do it yourself, which can save you both time and money.
Making the task even easier for the do-it-yourself hot rod enthusiast is the availability of complete powder coating kits, like the Eastwood Company’s Hot Coat system. It comes in two forms – Basic and Deluxe. The former includes an electrostatic air gun, powder reservoir and filter, plus a power control box that converts 110 volt A/C current to a minimum of 10,000 volts and includes a ground wire, a pressure regulator and air feed to hook up to a compressed air source and ½-lb. canister of gloss black powder. The Deluxe package includes all this, plus an extra cup of black, two additional colors, plus steel wire, high temperature masking tape and stoppers to prevent excess powder from getting in places it isn’t wanted, like threads and gasket surfaces. In addition, there are over 50 different colors of powder available, so it’s possible to paint any part of your hot rod in virtually any shade imaginable. According to Eastwood, all you need to start the powder coating process, in addition to the Deluxe kit, is access to a curing oven and a low-pressure compressed air source (between 5-8 psi).
Recently, Eastwood has also released a dual-voltage electrostatic gun that enables you to switch between 15,000 volts (more suitable for applying the powder coating to small parts), up to 25,000 volts, for covering larger areas such as frames and engine bays. Other companies that offer portable powder coating systems include Caswell Inc. and Chicago Electric Power Tools. Most of these kits sell for less than $300, which for the average enthusiast is money well spent.
We’ve touched a little on the advantages of powder coating already. When it comes to painting small parts and other greasy bits on your hot rod, it is very hard to beat powder coating in terms of time, cost and clean up. As long as the surface material of the part you are coating has been properly cleaned, there should be little or no problems. Using a mild alkali solution should help rid the surface of any remaining residues, such as grease, oil, and salt. When you apply the coating, the powder only needs to cover the surface of the part. Unlike paint, it won’t run or drip, and you won’t end up with an uneven finish (i.e. some areas of the part are more thickly coated than others). Compared to paint, once the powder has cured, it really does form a rock hard shell. You can try scraping it, scratching it or staining it, and as long as the bare surface of the part has been properly prepped, there should be no chafing or damaging of the finish. Powder coated bolts have been torqued with no damage to the surface, and engine parts have been coated with brake fluid and anti-freeze. A friend of the author powder coated the entire engine bay, chassis and most of the suspension of his Ford, and reported that all he has to do is spray on a little water, wipe off the residue and everything looks good as new. He’s driven the car over 6000 miles since completion, and both under the hood and the frame look just as good as the day he finished it in his garage.
Another great advantage to powder coating is that, because the granules are applied by electrostatic attraction, any existing material simply falls as dust. That means no drips or stains on the work surface or floor, and the excess can simply be brushed away. Unlike liquid finishes, which contain solvents to hold the paint particles together to coat a surface, the electrostatic bonding means there are no solvents required to coat the part and ensure the color sticks to the surface. Because of this, the risk of releasing Volatile Organic Compounds into the air is very minimal. It also means that no disposal of hazardous materials is required. In addition, if there is overspill, roughly 98 percent of the excess powder can actually be re-used, unlike solvent based paints.
Although the ease of application and minimal clean up make powder coating a very attractive option when finishing hot rod parts, the technology does still have a few drawbacks. For really fine detailing on specific parts, particularly interior trim pieces, or exterior details such as lamp housings, door handles, etc., it can be difficult to apply powder coating as a thin film. Below 60 microns, it is hard to achieve a complete coating of the surface due to the size of the particles. As a result, thin application of powder coating can often result in excessive amounts of orange peel, which partly explains why it is often used for parts requiring a thick coating to protect them from wear, such as engine components and frames.
Prep Is Essential
In order to achieve quality results, the surface of part you’re planning to powder coat must be thoroughly cleaned of all deposits, solvents and foreign matter. This is essential to ensuring that the electrostatic bonding of the powder particles to the surface actually works, much in the same way that car body shells are dipped in electrolyte on the assembly line prior to the paint process. If the surface isn’t clean, the particles simply won’t attach to it and you’ll be left with a patchy application of powder, no matter how much you’ve sprayed over the surface of the part. Also, depending on the material from which the part is made, care needs to be taken during the preparation surface. Parts can either be sprayed with degreaser, dipped in phosphate or sand or shot blasted. On many hot rod parts made from steel, such as frame cross-members, axle beams, control arms and even exhaust headers, shot blasting is often the most effective way of cleaning the surface prior to powder coating. Media blasting can also be used on glass and even some plastic surfaces prior to powder coating.
However, on softer materials such as aluminum, shot blasting can damage the surface, so it’s more effective to dip or spray the part in phosphates to clean it and promote greater adhesion during the electrostatic bonding process. Also, because aluminum is porous, it is often pre-heated before powder coating to remove any contaminants contained within the part. Otherwise, once the part has been powder coated and cured, these contaminants will show through the powder coated surface.
Although powder coated finishes are far more durable than paint, over time, they can still break down. One of the biggest problems is repeated exposure to ultra violet light, which will eventually break down the powder coating, causing the finish to fade like many automotive paints. In addition, if this happens and you want to re-finish a specific powder coated part on your hot rod, the old coating can be very difficult to remove. Most solvent-based cleaners have little or no effect at removing hardened powder coated finishes, so the most effective way is by media blasting or using commercial grade sulfuric acid. However, both these methods can damage the surface and structure of the part itself if absolute care is not taken.
Despite the drawbacks, it’s very easy to see why powder coating is becoming so popular in the hot rod hobby. Given the seemingly ever-tightening environmental standards on painting and hazardous material use and disposal, powder coating, with its minimal clean up, lack of VOC emissions and reusability, makes a great deal of sense when coating and finishing many parts in a hot rod project. And although it isn’t yet suitable for coating entire bodies, given the advances in powder coating technology in the last decade, perhaps a time will come when we will no longer need to use paint at all for finishing our favorite automotive custom projects.
The author and photographer would like to extend a very big thank you to Ray at Ray’s Radiator and Hot Rod Shop in Warren, Michigan for his assistance with this article.
The Powder Coating Process
Before beginning the process of powder coating, there are several things to consider. First off, you need to have access to a decent sized oven. Some auto enthusiasts who have their own workshops or garages often have a regular oven installed in them. Even if you don’t, make sure you have easy access to an oven, as it is an important part of the process. Larger ovens are also more versatile, especially if you’re coating larger parts like I-beams, cross-members and even wheels.
You also need to have access to a 110-volt outlet supply to charge the gun and an air compressor. Also, you also need to make sure that the parts being coated are supported by a metal surface so they can be grounded –steel hangers or grilles are often used. Once you have, the process can begin.
As mentioned, the parts must be thoroughly cleaned to remove any residue such as dirt, oil, grease or wax and then dried before the powder coating process can begin. Once the parts are dry and have been hanged or supported, make sure you plug or mask off any areas on the part that you don’t want to get covered in powder, specifically bolt holes, threads or gasket surfaces. Then, fill up the gun reservoir about ¾ full of the color powder you wish to use and screw it to the gun. Then, connect the air supply between the gun and compressor, setting it for a maximum of 8 psi. Plug in the electrical connector and switch on the 110-volt supply, and then connect the ground wire either to the steel hanger or grille supporting the part. Press the activation switch and the trigger on the gun. Carefully work your way across the part, coating inside edges first. Although it is much more difficult to cause runs in the surface than with paint, it is still possible, so try not to squirt too much powder on the part itself. Once the entire surface of the part has been coated in powder, release the trigger and turn off the voltage and air supply.
Examine the part under high intensity light. If you’re satisfied, place the part in the oven, which has been preheated to approximately 450 degrees Fahrenheit, and bake it for approximately 5 minutes. This will ensure that the powder flows out. Then, cure the part in the oven for approximately 20 minutes at 400 degrees Fahrenheit to ensure the powder turns into a hard, protective shell. During the curing process, the finish will change from a matte to a hard, glossy appearance. Once the 20 minutes are up, remove the part and let it cool. Then it’s ready for installation.
Ray’s Radiator and Hot Rod Shop
Given that most hot rodders like to use old cars as the foundation of their projects, many components required for the build will likely be showing the ravages of rust due to age and contamination by moisture and salt.
As with any coating, preparing the surface of the part is crucial to achieving good quality results. Here, a fender is sandblasted to remove any traces of rust, corrosion and blemishes.
Protective clothing is essential, including thick gloves, arm and neck covering and preferably a full head mask.
While some parts can simply be media blasted before the coating process, others need to be cleaned before applying the powder coat.
This long tube header is being spray cleaned. Many cast iron or steel parts with multiple bends and crevices can be cleaned using degreasers, then water, and then covered in phosphate to help the powder coat adhere to the surface. It must then be left to dry before the coating process can begin.
Some parts, particularly those made from softer metals, must be heated before powder coating in order to prevent contaminants within them from damaging the powder coating as it is cured. Preheating can also ensure that a part is completely dry after being chemically cleaned.
Now the actual powder coating can begin. The powder is forced through an air gun (also called a Corona gun) that uses an electrostatic positive charge to allow it to adhere to the surface being coated (which is grounded).
In automotive applications, powder coating is very good for use on items like valve covers, accessories and exhaust components like these long tube headers. Once it has cured, the coating is extremely hard and durable, with a much reduced risk of discoloration or damage. It can also be very easily cleaned, making it ideal for show cars that are regularly driven.
Once the parts have been coated, they are then placed in an oven. Initially, they are baked for approximately 5 minutes to ensure that any remaining powder flows out prior to curing.
Although this is an industrial-sized oven, powder coating can easily be done at the hobbyist level, and depending on the size of parts, a conventional oven will do. The oven needs to be heated to 400 degrees Fahrenheit and the parts cured for 20 minutes to achieve maximum results.
Powder coating can be used on any number of parts on your hot rod. On the front end of this project we can see that the headers, valve covers and even blower casing have been treated.
This upper control arm looks like a brand new piece, but unlike many steel items, the surface will not rust after a few months and it can be easily cleaned. Note the masked hole (powder coating can cause problems if it gets into areas needed for screws, bolts, bushings or gaskets).
Coil springs are a good candidate for powder coating, though care must be taken to ensure the entire surface is covered.
Intake manifolds are also become an increasingly popular item for powder coating, which helps preserve the finish. Traditionally painted intakes can become worn very quickly due to the wide range of temperatures resulting from the operation of an internal combustion engine.
More and more vehicle components are being powder coated today. Whereas once it might just have been the differential cover, the entire rear end assembly can now be treated.
And the finishing touch for many hot rod projects is a cool air cleaner. While many rodders use chrome or polished aluminum, a powder coated cleaner looks just as good and is easier to maintain.
Published Dec 7th, 2015