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07, Jul. 2025

How to Apply a Two Coat Powder Coating System

So you have your substrate, all prepped and ready and it is time to lay down some coating.

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There is a great selection of products available that offer protection and decoration. Some of these products can be used as a two coat system, so let’s dive right in and check two coat systems out.

At the basic level, a two coat system is a method in which two coatings are applied to the same substrate. The most common two coat systems involve laying down a primer, curing it, and then applying and curing a top coat. Sometimes, the first application is a color coat, with the second application being a clear top coat. Pretty simple, right?

Why Should You Use Two Coat Systems?

Two coat systems can offer some great benefits. Do you want the metal to rust, corrode, or oxidize? Of course not. A two coat system is one way to achieve great corrosion protection, as applying an epoxy or zinc rich powder primer beneath your top coat can do just that. This is an especially great option if you are working with steel, or have limited pretreatment available.

Two coat systems can also be used if designers want to add a bit of extra flair and pizzazz to a surface, perhaps in the form of a high gloss clear coat. Similarly, they may also want to add some further protection or functionality. For example, certain domestic appliance manufacturers add a fingerprint-free clear powder, on top of their chosen look, to improve the ability to prevent fingerprint marks.

Some powders come with the recommendation of a clear coat for exterior use as well. This is often true of special effects powders and can be a good idea to extend their corrosion resistance and life expectancy. However, it is important to note that for high grade, exterior architectural applications, putting a powder with basic exterior weathering capabilities down and then adding a clear coat designed to pass higher weathering specifications, will not increase the weathering capability of that first coat sufficiently to meet the demanding architectural specs.

Two coat systems can also help enhance colored coatings with bright pigments. For example, at T, IFS Coatings’ sister brand, to achieve the ever popular neon colors, we recommend laying down a white coating (crystal white) first and then applying the Polychem neon color. The combination of the bright white base coat with the neon on top really makes the color pop.

In fact, any sort of coating that has a special effect, like metallics, glow in the dark, and translucent will benefit from a base coat applied beneath them. There is a reason why artists paint on white canvases 90% of the time. A white base enhances the vividness of any color.

There are many more reasons why you might do a two coat system, like a thicker film build requirement to improve the barrier between the elements and the substrate.

There are some great advantages to two coat systems, so read on to discover the how’s and why’s.

The great thing about two coat systems is that they are easy to use – so anyone can perform them. So let’s check out the top tips for application and achieving the very best results.

Two Coat, Two Cure Systems

This method is likely very familiar to most of you. Laying down a primer or base coat, curing it, and then applying your top coat and curing that is a dance as easy as singing your A, B, C’s. This method is also used for a top coat and clears.

This process is easily applied after pretreatment – whatever the type of pretreatment you are using. After pretreatment, simply apply your first coat and cure it in line with Technical Data Sheet (TDS) requirements. It’s good to note that most of the time you will need a full or almost full cure on this first coat. Likewise, don’t overbake it. Overbaking the first coat can really affect inter-coat adhesion. Then simply apply and cure the second coat.

Watch the thickness of the base coat. Too thick, and you will have trouble applying the topcoat. Remember with powder coating, the electric charge will not pass through a thick base layer as easily as it would a thinner one (it always needs good ground).

Two Coat Systems: The Pros and Cons

Applying more product to a substrate may mean adding time and money to a job. Whether or not it is worth it, is up to you. The advantages in increased performance and product longevity are often well worth it though.

Plus, if you apply the first layer on too thick, you will either have an uneven – and likely unattractive – top coat or if you apply a clear top coat on too thick you will find that it turns milky. Not something you want to give to a client.

In the pro column, using a two coat system can be a pretty dang simple way to really enhance the corrosion performance of your coatings – not to mention the added benefits in looks and lifetime.

The Do’s and Do Not’s of Applying a Two Coat System

Below, we have compiled a list of tips that our tech service team have learned over their many years of applying powder. Like with any coating, experience helps, but some of it can be trial and error, so give it a go.

First up: Good ground is essential for clear coats. If you do not have good ground, you will have problems with starring or back ionization. Starring looks like you have a sand dollar on the surface, and they can be as small as a pencil eraser and as big as a dime. Back ionization gives the coating a rough look – more like a grapefruit peel than orange peel. This might mean cleaning excess or baked on powder from the racks and hooks so you have good metal to metal contact. You should aim for one megohom or less resistance to ground at 500 volts – you can measure whether or not you have good ground by getting an ohmmeter, which measures electrical resistance and you can pick one up for under $50.
Test any product (by itself or with another) on panels or pieces before coating anything for a client. That way you will truly get a feel for how the products work and can make any necessary adjustments before coating the part.
In pretreating, make sure the part is properly rinsed and dried. Also, do not let the pretreat simply dry in place. Leaving it to dry on its own means water spots can form. Even when you paint over these spots, you will see little dry spots underneath the coating and worst case scenario, these spots can even blister.
Many powder products may work as a two coat process but have not been designed as such. Conversely, many simply won’t work together. Unfortunately, learning what does and does not work together often comes down to trial and error. Staying within the same brand of powder for both coats at least allows you some consistency and enables you to check with the manufacturer for recommendations if problems occur.
Do not overbake in between coats. Doing so can cause inter- coat adhesion problems.
Remember, with two coat systems the thicker film build also reduces the ability of the top coat powder to take a charge. Good film thickness is key.
Similarly, it is tempting to do so, but do not lay on a clear topcoat thickly. It’s easy to do as clear coats often apply well, but the thicker you apply a clear coat, the less clear it becomes, often taking a milky coloration. You may not even realize you’re doing it, so be careful. Investing in a film thickness gauge will enable you to quickly check and measure the exact thickness of a coating once it has been cured; you can pick up a decent gauge for a few hundred bucks.
Check the cure requirement of both coats. Are both low cure formulations or is one a regular cure and the other a low cure? You need to take this into consideration and adjust your cure schedule accordingly. For example, if you’re using a regular cure primer, make sure it’s fully cured or almost fully cured before you apply a low cure top coat. If you don’t, the primer won’t perform as it’s designed to as it never fully cured.
Another common sense tip here, but do not let the product get contaminated – both in its container or while it is on the substrate, especially between coats. Dust, dirt and even the oil from your hands can cause trouble down the line – from starring to leaving a fingerprint on the paint - and then you end up sealing it in with a clear topcoat. So, don’t leave too long between applying coats and do not handle the substrate between applications or cures. Keep your products sealed in their containers when not in immediate use.

A lot of these tips that we have covered come will a fair bit of trial by error, not all ovens work the same and nor do all metal substrates accept the product in the same way. The great thing about powder coating is anyone can do it and the more you do it, the better you become. The more experienced you are, the more likely it is that most of this will be second nature to you.

Dry On Dry

The Dry on Dry, or CoCure process, has picked up in popularity over the last few years. A CoCure or dry on dry process involves pretreating the part as usual and then applying your first coat. Then, without curing the first coat, apply your second coat. The final step sees both coats cured together.

Pros and Cons

It certainly has its advantages, including reducing the need to move parts in and out of the oven which of course comes with the risk of contamination, and less time and energy spent in the application and curing process. Cycling through the application, curing, cooling, testing process adds time and money to any job. A dry on dry two coat system can save you both, by, essentially, cutting out the middleman.

The not-so-great aspects of this two coat method are that you can’t just slap any two primers and topcoats together and have it work. You may get lucky, but the only way to achieve guaranteed results is to use products that are formulated to work together in a dry on dry process. Otherwise? You may get a peeling, cracked mess of a coat. Not a good end game.

Adjust the KV settings on the guns between coats. Lowering the KVs when applying the primer and then readjusting the settings higher again for the top coat can help reduce the chance of back ionization or KV rejection. Play with it and see what works best on your system.

What’s more, applying your first coat of powder while the part is still warm from the dry-off oven can help attract the powder and actually cause it to gel slightly, starting the cure and quickening the process. This is especially true if you’re working with thick or heavy parts.

Conclusion

A two coat system is a great way to enhance and protect your substrate, either from the weather or from sticky fingers. Some powder coatings are designed as two coat systems, others simply happen to work together. So often, deciding to use a two coat system will depend on what you are coating and what you need the product to achieve. Using steel and looking for improved weathering? That zinc rich primer and top coat designed for exterior applications are a no brainer. Looking to achieve that bright neon glow or extreme chrome effect? Get that bright base coat down first. There are many great two coat products available.

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Three-Coat vs. Two-Coat Paint Systems for Buildings

More is better right? For many architects and building owners, the decision of three-coat vs. two-coat paint systems certainly isn’t black and white.

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What’s the Difference?

As the name implies, one system has three layers of coating (or film), and the other consists of two-coating layers.

Most often, a two-coat system includes the primer and a top coat whereas three-coat systems include the primer, top coat, and a third coating (most often a clear coat) that is applied over the top.

So while the apparent difference involves the number of coating layers, there are other important differences. When the coatings are applied, two-coat systems can be produced in one pass through commercial coil coating lines, whereas three-coat systems routinely require a second pass through the coating lines.

Additionally, two-coat systems tend to be industry standard for most manufacturers, while three-coat systems are most often considered a special order. As you might guess, these last two nuances can carry both cost and lead-time implications.

Are 3 Coat Systems Necessary?

For the vast majority of colors, a two-coat PVDF system of a primer and a topcoat are sufficient. There are, however, times when a three-coat PVDF system, primer, color coat, and clear coat is necessary to improve the color retention and chalk resistance of the solid color or metalescent base color.

Saturated colors like reds, oranges, and purples are good examples of colors that may benefit from the addition of a clear coat. A clear coat may also be needed for some metallic colors, like bright silvers, to protect the aluminum flake from losing its brightness and turning dark. Lastly, there are some special effect coatings available on the market that may also require three-coats; a primer, a base color coat, and an effect coating. Click here to learn more about this unique group of products.

Outside of these situations (saturated colors like reds, oranges, and purple; bright silvers and special effect coatings), three-coat systems are rarely necessary nor beneficial.

Lead Times & Minimums

As mentioned earlier, most manufacturers consider three-coat systems a special order. Consequently, they involve longer lead times and minimum quantities. For large projects, minimum quantities are often considered a non-issue; however, even if the original order easily meets the guidelines, it’s important to remember that replacement panels or small amounts needed for building additions or modifications at later dates can be problematic.

Material Cost

Material cost is a consideration in almost all projects. Two-coat systems can be applied in one pass during the coil coating process, so they certainly offer a lower initial purchase price than their three-coat competitors. Admittedly, part of the higher cost is due to raw material costs for the third coating layer.

But what many people don’t realize is that the larger cost increase stems from the fact that the entire coil needs to go through the coating line a second time. At first blush, that may not seem cost-prohibitive, yet due to increased mill time, higher reject rates for three coat systems, and the extensive line clean-up required after clear coat applications, the additional cost can be 300-400%.

Consequently, the increased project cost is a given when specifying a three-coat system, so the decision shouldn’t be taken lightly.

Performance

To address performance, let’s start by looking at warranties. Three-coat systems don’t offer a longer or better warranty, which would indicate that their expected performance is similar to a two-coat system. After all, if it’s truly a better product, one would expect a better guarantee from the manufacturer.

In chatting with a technical representative from Sherwin Williams recently, he summarized it like this: clear coats are like a light switch. They either provide a notable improvement in a coating’s performance, or they make little to no difference in the performance of the coating. So the good news is that we’re getting closer to that black and white decision.

In cases of the saturated colors mentioned earlier, three-coat systems can certainly provide a benefit. Still, for earth tone colors, which represent the majority of projects, three-coat systems tend to be unnecessary and drive project cost and lead-time up.

With that said, it is possible that projects located in highly corrosive environments may experience a slight benefit simply due to coating thickness. It’s not that three-coat systems necessarily perform better in these harsh environments. Rather, the overall coating is thicker so the theory is that it can take a bit longer for mother nature to break the coating down to the point of failure.

It’s important to note, however, that there isn’t empirical data to support this concept. Consequently, instead of black and white, the potential gain is gray at best. While a three-coat system might outperform a two-coat system in these harsh environments, it still doesn’t mean they are the optimum choice. Check this out to learn more about selecting the best coating options for different types of corrosive environments.

Color Selection

In talking with Architects, we’ve learned that one of the primary reasons they specify three-coat systems has nothing to do with performance. Instead, they simply want to ensure that their building owners are able to pick from a full-color selection, including micas and metallics.

Since many manufacturers (McElroy included) offer their metallics in a two-coat system, requiring a three-coat simply to gain access to the metallic families represents an entirely unnecessary cost increase.

Specification Tips

When the goal is simply to gain access to a full standard color offering, including metallics, a three-coat system isn’t necessary. Instead, using the phrase “manufacturers full standard colors including metallics” in the project specifications provides the architect with the protection to avoid post bid upcharges without adding the unnecessary cost of a three-coat system to the project.

It is important to note that most manufacturers offer at least one standard red color; however, purples and oranges are rare to find on manufacturers’ “standard” color offerings.

Consequently, if these colors are desired, it’s best to indicate “custom color 3-coat system” in the specifications to ensure accurate project bidding.

When there is serious interest in a three-coat system from a performance standpoint for corrosive environments, another specification tip is to write the base bid as a two coat system with an alternate add for the three-coat system. This approach ensures the true cost upcharge for the three-coat system is realized.

Faced with real numbers and limited to non-existent performance gains, few architects chose to move forward with a three-coat system. But if they do, at least it's with a full realization of cost vs. potential benefit. Given this same scenario, some specifications use the three-coat system as the base bid and request a deduction for going to the industry standard two-coat system.

As might be expected, the total cost savings are rarely achieved by approaching from a deduct perspective.

Summary

In summary, the first consideration for a two-coat vs. three-coat system should center around the intended colors. Certainly, for projects involving saturated color families like purples and oranges, it may be prudent to have a three-coat system specified as the base bid.

Outside of saturated color families and bright silver metallics, most would agree that while a three-coat system might perform incrementally better than a two-coat, the differences are minimal and rarely (if ever) offset the additional project costs and lead-time.

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