To Urethane or not to Urethane:
The ABC’s of Clear Coating by Craig Fraser

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Reprinted with permission from Airbrush Action (February 2000)

It’s the first thing you see and a paint job’s last line of defense. In the kustom painting field, there’s probably nothing as under-appreciated, yet as important, as the clearcoat. Today, kustom paint clearcoating is not just a good idea–it’s a necessity. Considering that 99 percent of all show-quality graphic jobs out there are 2-stagers (2-stage basecoat urethanes, that is), it’s a safe bet that, after the graphics have been completed, the final piece of artistry to apply is the clearcoat.

Although some people may not consider the spraying of clear to be an art form, I guarantee that their outlook will change completely after trying to clear something themselves. There’s a common paint industry phrase that states, "Behind every good clearcoater, there’s a better buffer." It may be true in some circles, but clearcoating remains an easily attempted, rarely mastered, art form. While many airbrushers refer the clearcoating of their masterpieces to an outside party or in-house professional, it is still important that every airbrusher understands, at the very least, the basics of the clearcoat.

Urethane Clearcoating In Today’s Automotive Market

Although there are a variety of synthetic enamel, lacquer-based, water-borne and even water-based urethane clears floating around, the "big boys" on the automotive paint industry block are the solvent-based polymers known as acrylic urethanes and urethane enamels. While all automotive paints share the same technological roots, modern day urethanes take advantage of the most current innovations in polymer technology. Now, I’m definitely no chemist in this field–let’s just say that, as far as clearcoating goes, I’m a good airbrusher. Keeping that in mind, I generally leave clearcoating up to my partners in crime at Kal Koncepts, Dion and K-Daddy. And, since the basics are the only things that remain constant in this field, I’ll try not to toss around too many five dollar words. (Mainly ‘cause, like most of us painters out there, the lab-coat techie-talk leaves me feeling like a combination of Rainman, Forest Gump, and Billy Bob Thornton in Sling Blade...get my drift?)

What Is A Clearcoat?

The clear in a paint job is basically the protective coating sprayed over a 2-stage basecoat. It not only protects and seals the paint, but it also gives the final paint job its overall gloss and deep shine. All automotive final clearcoats fit into the catalyzed clear category.

In the acrylic urethane field, an isocyanate-based catalyst is used to harden the clear, much like the catalyst in epoxy cement hardens the resin. When the catalyst is mixed with the urethane resins and reducing solvents, the chemical reaction causes heat, a necessary ingredient in the drying process. While all urethanes should be considered toxic and require proper ventilation and the use of respirators, isocyanates are the main bad guys. As a nerve toxin, isocyanates are not to be toyed with–they absolutely require the use of professional respirators at all times. I recommend using a dual-cartridge, active charcoal respirator rated for organic vapors. Isocyanates have no color, taste, or odor. For complete protection from long-term exposure, OSHA (the Occupational Safety and Health Administration) recommends using fresh air in the work environment whenever isocyanates are present.

Although many folks consider the clearcoat to be a separate system in the paint process, it is actually an incorporated element that is crucial. In a classic 2-stage system, the basecoat is the first stage and the clearcoat is the second (hence the name, 2-stage system). Single-stage paint is a catalyzed paint with the clear built right in. Since it’s primarily used for single-color paint jobs and rarely, if ever, found in graphic jobs, we’re going to ignore the single-stage paints for our purposes here.

A 3- or 4-stage system is something different. Extra stages are used to describe additional clearcoats containing either a mica-based pearlescence, an applied kandy, or a tinted clear shot over an existing metallic, with a final coat of transparent clear to finish the job. For these types of paint jobs, the clearcoat transcends its protection role and actually becomes a visual effect, with the embedded pearls, flakes, and kandies. Perhaps the easiest way to spot a multiple-stage paint job is by the illusion of depth, created by the number of coats of transparent kandies or clearcoats. The more clear placed on a painted surface, the greater the paint job’s ability to trap, reflect, and amplify light. These traits can be enhanced with the use of metallic bases, metal flakes, and pearls, which can be added to the clear to give the clearcoat a prism-like ability to modify light.

With urethane basecoat systems, the clear’s topcoat acts as a light transport, bringing to life all of the embedded details and colors in graphics and murals. This reactivation of the urethane toners by the clearcoat is possible only in compatible systems. This is one of the strongest arguments for using basecoat systems over water-based colors in auto-motive kustomizing. Water-based colors can’t provide the depth and brilliance, because they can’t combine with the current urethane clearcoats. Because of the hardened resins and high DOI (distinctness of image) factor, today’s urethane clears can be buffed and polished to a mirror-like finish, unlike the older modified alkyd enamel systems that, while they served their purpose in their time, had yellowing problems. Urethane clears are reserved not only for automotives, but I’ve found them very handy for painting on guitars and other hard surfaces, such as carbon fiber, fiberglass, and floors. Because of their flexible nature and UV absorption, they’ve recently been experimented with as a sealer and protective coating for airbrush effects on vinyl substrates.

HVLP and Other Acronyms

The weapon of choice for today’s hot-shot clearcoaters is the HVLP (High Volume Low Pressure) spray gun. In most states it’s not just a great idea—according to the VOC (Volatile Organ Compounds) boys, it’s the law. HVLP guns apply a higher volume of material with less overall nozzle pressure, which results in less overspray waste and more material on the surface. These guns are not only more environmentally friendly, but they are an advancement for the painting industry with regard to spray quality. They can maintain a wider, more uniform fan of material (up to 17 inches in some cases) and a material transfer percentage of anywhere from 70-90%. It’s a vast improvement over the 20-30% efficiency of older siphon-feed, non-HVLP models. HVLP spray guns are available in siphon- and gravity-feed models. Many professional painters prefer gravity-feed spray guns because of the higher-volume rate of flow and because having the color cup mounted on top provides added clearance under the gun (which makes shooting car roofs easier on the wrists).

While its external appearance hasn’t changed much, the automotive spray gun has gone through more internal design changes in the last five years than it did in the previous five decades. The number of gun manufacturers has also increased. Deciding which one is best is merely a matter of personal preference. The important thing to remember is that the gun doesn’t make the artist, it just makes his job easier. I believe that, as long as you stick with known brands such as Iwata, Binks, Sata, and DeVilbiss, you can’t go wrong. Sometimes it’s your local distributor who makes the decision for you. After all, what good is the ultimate spray gun, if you can’t get any rebuild kits for it? Often times, your local jobber will let you borrow some of a demo gun before buying it, to see which one best suits your painting style.

Clearly Speaking

With automotive paint research at a record high, you’d think that clearcoating would be getting easier, but it’s really just the opposite. It might even seem as if an automotive painter needs a Ph.D. in polymer chemistry just to be competitive. (I’m joking, but it’s one of those situations—if you don’t laugh at it, you’ll probably cry.) Sometimes, it appears that the technology caters more to the mechanized painting industry than to the human painter. Many of the new clears have very small windows for error; if a problem occurs, the remedy is not a touch-up, it’s a re-paint (curiously, an assembly line solution). Lucky for us paint minions, industry gurus such as Jon Kosmoski and his company, House of Kolor, have proven that man does not live by factory colors alone. With a line of innovative finishes and fantastic pearlescents (not to mention killer clears), his small company has managed to carve out a kustom niche that many bigger companies are also rushing in to fill with their own lines of kustom paints, pearls, and kandies. Though radical ten-color paint jobs and three-gallon clearcoats may not be the industry norm, they sure do look good on paint shop calendars, and they definitely help sell a paint line.

In addition to catalyzed clears, there are a whole batch of air-dry clears that have become known as "intercoats." These intermediary clears, distant cousins to the old air-dry lacquers, are designed to be sprayed on in between colors to protect them from color bleeds, promote adhesion, or as a fast drying carrier for a pearl or kandy tint. The air-dry interclears are still urethane-based and require solvent for reducing, but since there is no catalyst involved, they do not have the structural integrity of the catalyzed clears and cannot be used as a top coat. Because of their non-structural strength, it’s actually a good idea to limit the number of coats to four. Otherwise there could be adhesion problems and structural cracking. House of Kolor’s SG-100 intercoat clear is an excellent protective interclear and a good balancing clear for mixing batches of Kandy Koncentrates and urethane toners. This balancing clear acts as a structural glue for the toner pigments and a flow enhancer. All of the transparent kandy colors I use in my murals and graphic airbrush effects contain SG-100.

There are a variety of books and paint articles defining the art of painting and clearing and, if you’re looking for an alternative to the written word, there are videos available. Jon Kosmoski has had an automotive video series on the market for years and, at Kal Koncepts, we have a four-video automotive painting and airbrushing series available through Airbrush Action. All in all, probably the best advice I have is to experiment.

Conveniently, most clears that are illegal in your area will be unavailable and as far as mixing ratios go, the labeling is usually pretty self-explanatory. The art is not how to follow instructions, but how to modify them for your individual use. For example, since temperature is a major variable, the clearcoater’s use of the proper reducer in the proper amount can have a great effect on the final finish of the piece. Such factors as assessing the gun pressure, the possible use of an accelerator to increase drying, the number of proper coats to attain a flawless finish, and the window between wet coats can be followed from the instructions, but need to be experienced first-hand to be truly enjoyed. To sum it up, your best bet is to find an accomplished painter and pick his brain. At my shop, I’m lucky to be able to yell next door to Kal Koncepts and ask K-Daddy or Dion, who’s a third generation car kustomizer, to get my questions answered. Granted, you don’t have Kal Koncepts a stone’s throw away—that is why the first piece of equipment in your shop should be a telephone. I spent at least an hour on the phone with Pete Santini and Jon Kosmoski before writing this article. (I edited out about half of the technical jargon and colorful metaphors, since it caused me to go into college chem-lab withdrawals). I mean, what’s the worst that can happen—someone hangs up on you?

Another good possibility for hands-on learning is the local training programs sponsored by your local jobbers. Frequently, House of Kolor/Valspar, DuPont, PPG, or the other big paint manufacturing companies put on training seminars that are literally designed to bring new painters up to speed and expose veterans to the new paint systems and spray technology. A little creative pleading can often get your local jobber to pay for your attendance. In addition to the excellent knowledge you’ll pick up, you have a chance to spray the newest clear systems and get a really swell diploma to hang above your desk to make you look important!

Well, I hope this article has, if not sparked your interest in the art of automotive clearcoating, then at least provided some insight into this highly competitive and specialized field. The general consensus among Jon Kosmoski, Pete Santini, Dion, K-Daddy, and all the other spray gun gurus I’ve spoken to is to get your feet wet—get a spray gun and go for it. I think everyone should try clearcoating their own work at least once, but if you’re looking for quality of finish and profit, hire a professional. Even if you have an in-house clearcoater like I do, picking up a gun and spraying will give you an appreciation for the art and will make you a better automotive painter or airbrusher because of it.

About the Artist

Craig Fraser operates the Air Syndicate airbrush studio in Bakersfield, CA, and is the in-house airbrusher for Kal Koncepts. He is a contributing editor for Airbrush Action, and a member of the Airbrush Action Getaway staff. K-Daddy, D-Bob, and Dave make up the rest of the Kal Koncepts krew, demonstrating in the photo what can happen to you if you don’t wear your mask when using the new clear systems. (Jesse, "Pup" Dowel is sitting in place of Dave on the right, since Dave is outside getting some fresh air and having a cig.) Paint to live, live to paint.