DIY Powder Coating
Posted: 28 February 2020
My journey with DIY powder coating started just over 18 months ago. I live in a home built in the mid-1980s, where many of the original fittings are no longer manufactured. Curiously, many of the parts used during the 1970s have remained available to this day. After 30 years, the window latches were looking worse for wear, with the original powder coat flaking off or bubbling. These latches, of course, were no longer manufactured. Doing some quick calculations, I established that it would be cheaper for me to purchase a sandblasting cabinet to tidy up the existing latches than it would be to replace these with modern equivalents. This is true even if I had installed the cheapest and likely lowest quality latches from one of the big-box stores. Add to that the hassle of having to re-drill holes in every window frame to fit a different type of product and the choice to remove, strip, paint and reinstall looked like it might have been the best way to go.
I could have simply sandblasted and repainted with spray paint, but I felt this wouldn’t be durable enough to stand up to regular use and the environment. Powder coating was clearly a better choice. I decided to investigate purchasing the equipment I would need and was willing to spend a few hundred dollars on a powder coating gun (goodbye savings from the DIY approach), until I stumbled across a low-cost tribostatic powder coating gun.
Tribostatic guns contain no electronics, instead they use friction to charge the powder as it leaves the gun. It is claimed they give a smoother finish with thicker coats and can apply powder to more complex shapes as they do not exhibit the same Fariday Cage effects corona guns do. The downside is they have consumable parts (i.e. the charging rod). In a DIY environment, the consumable parts are going to last a very long time, possibly a lifetime. While writing this blog post, I also saw claims that tribostatic guns are difficult to clean. This is simply not true. In the case of the Nordic Pulver NP-11 gun I selected, cleaning requires no more than for me to unscrew a tube, pull out the charging rod, and give the pieces a quick blast with compressed air. That’s it. Nordic Pulver also has a complete list of replacement parts for their guns, should I ever need them.
Since obtaining the gun, I have powder coated numerous items around the home, ranging from tea pot stands to outdoor light fixtures. If it needed painting (or in some cases, didn’t), it’s metallic, and small enough to fit in the oven, I probably powder coated it.
Getting started
To get started with powder coating, you require the following:
An air compressor. Unlike spray painting, powder coating doesn’t require a significant volume of air. I can powder coat comfortably using a 4mm inner diameter flexible air hose. Nordic Pulver recommend a meagre 2hp compressor with a 24L tank for their gun, which is similar in specifications to the smallest (and cheapest) units available from the local hardware giants.
A powder coating gun. My selection essentially came down to price. After deciding that a tribostatic gun was right for me, I had to find one at a reasonable price and of good quality. Nordic Pulver also offer a cheaper hobby gun, however, I felt the extra money spent on the higher quality tool was justified. If you are interested in a carona gun, US customers will find a range of these at reasonable prices, from the likes of Eastwood or Amazon. Being in a country with 230V/50Hz power, importing one of these units simply wasn’t an option.
You can forgo both the air compressor and gun, along with quality, if you buy one of these.
An electric oven. The size of items you can powder coat is limited by the size of your oven. You don’t need to go to any great expense, but don’t use your kitchen oven. I use a cheap 60L portable oven.
Powder. This is probably the most difficult to obtain component of powder coating. Unlike solvent-based paint, power coating powder is not something you can pick up at any hardware store, and where you can, your choice of colours will be limited. Locally, I can only purchase in 4kg or 20kg quantities, so I have thus far only purchased colours that I use a lot of, or specialist colours to match other powder coated surfaces. As a regular online shopper, I assumed I could simply visit AliExpress or eBay and buy small quantities of any powder I’d like. Not so it seems. Searches turn up numerous paint powders in the form of pigments, not powder coating powders. I have found suppliers via Alibaba who were willing to mix and match colours to meet a minimum order quantity, but once shipping is added, it becomes prohibitively expensive – unless you’re ordering pallet loads. The most reasonable price I’ve found for powders in small quantities, again with consideration to shipping costs, is Prismatic Powders. They have an incredible range of powders and will ship internationally for a reasonable rate. I intend to purchase smaller quantities from them going forward.
As a general rule, powder coats don't mix. If you mix black and white, you get black and white. I have had pleasant results mixing darker colours in arbitrary ratios, solely for the purpose of using up leftover powder.
A dust mask and eye protection. Common sense.
Miscellany. I recommend a flexible air hose with water trap and regulator at the tool end. I also suggest purchasing some sort of stand on to which you can place the oven trays or racks on to apply powder and allow them to cool. I use an old keyboard stand. For the environmentally conscious, you may also wish to look in to a means to capture the powder. While powder coating is considered less harmful to the environment than solvent-based paints, we should avoid adding more microplastics to the environment if we can.
Process
As with any form of painting, a quality finish starts with the preparation. I am typically dealing either with new or freshly sandblasted metal objects, so my main concern is that the item is clean. You can powder coat over some existing finishes, but contaminants may result in a poor outcome. Search for ‘outgassing’ for more information on the causes and possible solutions.
If you find yourself needing to fill holes in objects prior to powder coating, the original JB Weld works well and will withstand the temperatures required for curing.
Every item I powder coat is cleaned with grease remover and only handled using gloves thereafter. On occasions where I have touched metal objects with my hands, the results haven’t been disastrous, but I stick by my advice not to touch the item once degreased.
Most items are coated by hanging them underneath the oven rack. I’ve found 0.041" (1.04mm) stainless steel lock wire to be ideal for this. I have numerous offcuts of this from using my ClampTite tool to maintain air and irrigation hoses. This wire is rigid enough to hold items through holes, minimising contact with the object and therefore the size of any unpowdered region. Thinner wire will often bend, resulting in contact with the surface being coated, not just the edge of the hole. This wire, when bent, is also strong enough to spring back and holding many items in place through friction. This approach is ideal when the inside of the object isn’t being powder coated and leaves no blemishes on the coated surface.
When multiple items are being powder coated, I will often join these with thinner gauge stainless steel wire and connect the earth wire of the gun to the common wire. Being thin, this allows more freedom to move around with the gun as the clip will remain attached even if the joint is flexed. More importantly, this wire provides electrical conductivity between all the items being coated. Relying on the metal rack or tray to provide this isn’t a good idea, especially as thicker layer of powder builds up with repeated use.
Masking is an important aspect of powder coating. Unlike spray paint, powder will find its way on to surfaces not in the direct path of the gun due to the static charge. Threads are one area where a thick coat of powder is undesirable. Internal threads can be protected using various sizes of silicone stoppers. For external threads I use PTFE tape (plumber’s tape) as this will withstand curing temperatures. High temperature tape such as Kapton can be used, but may be difficult to remove if powder is applied over top. While some people use masking tape for partial cures, prepare for a sticky mess of adhesive if it’s left in the oven too long.
When spraying, I prefer a slow and steady approach. I start about 18" away from the object with a low pressure on the gun, or with the air completely off, increasing the pressure until I achieve a flow rate I am happy with. This is why I favour having a regulator on the tool. While doing this, and every time I start spraying thereafter, I point the gun to the side of the object. This avoids any powder already applied from being blown off by the initial burst of air. Likewise, if I were to get too close, I could blow powder off the object. Carona guns often have a diverter tip which may prevent these issues. Letting the static charge pull the powder to the object works best.
Pay attention to deep areas and concave curves. You may need to point the gun at these areas for a little longer to penetrate these areas. If you are using a carona gun, adjusting the power may help with this. Once you’ve finished, carefully inspect the item for areas which aren’t properly coated. Any deficiencies apparent now will almost certainly be visible in the final product. If you miss a spot, another coat could be applied later, but it’s best to address this now. A torch or other light source that can be moved around the object will help with detecting missed spots.
Curing requires heating the object being powder coated to a set temperature for a fixed period. The time starts when the surface of the item reaches the required temperature. Many online guides will advise you to start the time when the powder starts to flow. This approach seems to work well, although I tend to bake for a few minutes longer to be on the safe side. Incorrect temperature can have a detrimental effect on the finish and cause issues such as the paint being too brittle, so it’s best to follow manufacturer guidelines and verify the temperature using a thermometer. An IR thermometer allows you to check the object being coated has reached the desired temperature and is more accurate than the oven temperature, although I stopped using one myself after verifying the thermostat was accurate and adding a few minutes to the cure time.
A method to coat items which aren’t metallic is to apply powder to the pre-heated item. This is called hot flocking. I’ve only used this method once, to correct blemishes in powder coat resulting from not cleaning an item thoroughly enough after sandblasting. I believe I missed a small spot of dust and it showed though bright white after powder coating. A quick blast of powder on the hot item and re-curing hid my mistake.
DIY powder coating is both practical and inexpensive. With an initial outlay of less than $US200, assuming you already have an air compressor, you can purchase everything you need to be powder coating at home.