Jerry Gustafson’s RV-8 was painted by Kracon in a delightful Flying Tigers P-40 scheme.

In Search of … the Perfect Paint Job Part 3: Preparation for Your Creation: Metal and Composite Construction. BY RICK LINDSTROM

n the last two installments of this series—KITPLANES® May and June— we have looked into the tools and expertise available to help you create a pleasing design and have provided a survey of some of the new paint and applicator technologies on the market. Now it’s time to get more specific and examine what’s involved in painting metal airplanes.

I

Make Mine Metal Kracon Aircraft Refinishing is an aircraft paint shop in California’s Sacramento Valley founded by Edwin Krass and Rob-

ert Coon in 1972. With many hundreds of painted aircraft to their credit, from RVs to Citations, Kracon prides itself on an ever-growing list of satisfied customers. They’ve also amassed a wealth of knowledge along the way. “Aluminum is a very active metal; it doesn’t take long to start corroding,” Krass says. “I’ve even seen surface corrosion start where someone has marked on the airframe with a pencil or something, and then riveted it together, and it corroded right along those marks.”

Photos: Rick Lindstrom, Courtesy Jim Clark, Jerry Gustafson, Aircraft Finishing Systems

Krass stresses that surface contamination of metal airplanes is one of the most frequent obstacles to getting that perfect paint job. Because it’s typical for metal airplane builders to fly off the hours in bare aluminum livery, he frequently sees airplanes show up for painting in desperate need of a thorough cleaning before any further surface preparation can occur. Some of the contaminants that deserve extra attention in removal are lithium grease, anything containing silicone and many types of spray lubricant. A strong solvent, such KITPLANES July 2005

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time power tools cause bits to fly, and gloves should be worn any time you’re using irritating chemicals.

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as Methyl Ethyl Ketone (MEK) may be needed (along with some elbow grease) to remove all traces of these chemicals from the metal to be painted. “Make sure you use a clean, fresh rag to wipe off the MEK,” Krass adds.

Dents and Other Obstacles: Part Of Life “I’ve never seen an absolutely perfect airplane,” Krass says. “So we usually figure on at least 4 hours of bodywork on any paint job we do.” A lightweight polyester filler, available at most aviation supply houses, should be used to fill in those unfortunate realities inflicted by a dropped tool or other mishap. The surface under the filler needs to be scuffed up a bit, since the filler needs a good mechanical bond to attach itself to the metal. Krass recommends using 100to 180-grit sandpaper for this task. Once the depression has been filled and the material has cured, the excess filler can be smoothed down with a dual-action sander, ending with 220-grit sandpaper. If you’re fortunate enough to live in an area where spraycan lacquer primer is still available, this can be successfully used on top of the

Cleanliness Is Next To...

Yes, we know it’s not a homebuilt. But this Cub was painted with Aircraft Finishing Systems’ waterborne urethane paint. It sure looks good from here.

filler. Otherwise, Krass recommends using a two-part catalyzed epoxy primer. “Most other spray-can primers just don’t have the solids needed for a sufficient build, so why take shortcuts?” Protruding rivet heads love to catch foreign materials where they meet the skin, and cleaning thoroughly around them can be a challenge. If your small brass wire brush doesn’t do the job, try using a small Scotch-Brite wheel chucked into a rotary air tool can help speed things along. Care should be taken not to gouge the surfaces needlessly, but the visible scuffing of the metal is normal and will disappear under a good primer coat. Of course, protecting your skin and eyes is an important part of the process. Proper eyewear is essential any

Once the dings have been filled, smoothed and primed, it’s time to prepare the metal for paint. Kracon starts with a good alkaline-based cleaner, such as tri-sodium phosphate (TSP) to knock off the bugs, grease and minor contaminants. Then, a phosphoric acid solution is applied to etch the metal, followed by treatment with a chromate conversion process (trade names Alodine or Iridite, but commonly referred to as just “alodine”) to prevent corrosion and create a good base for the paint to adhere. These are the wet stages, each requiring a good rinse with clean water after each step is completed. Both the phosphoric acid etch solution (such as Alumiprep) and alodine are usually applied manually. Kracon recommends using a red Scotch-Brite pad to rub the phosphoric acid solution into the section of metal being prepared, scuffing the surface as you go. Before it’s allowed to dry, it should be rinsed from the section with fresh water from a hose. “You can easily tell when you’ve got all of the surface contaminants off,” says Krass. “The water just sheets

Jim Clark’s beautifully detailed RV-8 was also painted by Kracon...no surprise when you learn that Clark and Gustafson (previous page) are neighbors in Napa, California. Both airplanes, incidentally, are powered by Powersport 215 rotary engines.

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Ed Krass, co-founder of Kracon Aircraft Refinishing in Lincoln, California. He’s smiling because he’s figured out the thousands of tiny details that make the difference between a good paint job and a show winner.

off the surface. If you see any kind of ripple or beading, you’ve still got something underneath that needs to be removed.” This is closely followed by the alodine treatment, and it’s not necessary to wait for the water rinse to dry. In fact, the sooner the alodine is applied after the etching solution, the better. If you’re working alone, you’ll probably want to treat a single, manageable section with both processes before moving on to the next. The alodine solution is usually brushed on and then rinsed off after five to 10 minutes. Available with or without a gold tint, it’s easier to see where spots have been missed when using the tinted variety. It will also stain your skin, so be sure to wear gloves and other protective gear. Surface streaks should be expected, and have no negative impact other than their appearance. After a good rinse with clean water, the freshly alodined surface needs to air dry before it can be primed. “It’s best to shoot the primer coat as soon as possible after the alodine,” says Krass, “ideally, within a few hours after it dries.” If you haven’t already masked off the areas that won’t be painted, this would be a good time to finish this step.

Whew! If this sounds like a lot of work, you’re right—it is. But this is how the painting pros at Kracon achieve such predictably good results with metal airplanes. Is there an easier way? According to the folks at Aircraft Finishing Systems KITPLANES July 2005

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of Missoula, Montana, there is. “With our finishing system, everything from start to finish is with either water-based or waterborne products,” says AFS technical guru Dan Stewart. “And that’s a huge difference, because solvent-based glues, thinners and paint are all hazardous—plus the cost of HAZMAT shipping.” Originally developed as the final steps in finishing fabric-covered aircraft, composite and metal aircraft can benefit from the AFS product line as well. Metal aircraft surfaces can be cleaned and acid-etched with the single-step Aluminum Etch and Cleaner,

This is some of Kracon’s work on a Cessna rudder. The dark spots are where indentations have been filled and sanded smooth. Once the primer coat is on, you’ll never see the color change.

Krass uses a Scotch-Brite wheel to rough up the area around rivets to make sure the primer has a good bite and to ensure that no grit or debris remains behind.

and then primed with the AFS Primer Sealer, which does not require a catalyzing agent. “Alodining is optional,” says Stewart. “If I were going to leave some parts sitting around for awhile, I’d alodine them. But we recommend going right to the primer sealer after cleaning and etching.” For composite and fabric airframes, AFS recommends its CecoFILL high-build primer that also provides UV protection through the use of flumed carbon in a water-based latex material. According to Stewart, the best results are obtained by using between four and six light spray coats on the surface, each applied 90° to the previous one. Typically, sanding can be started within an hour of applying the last coat, and top coat application should be applied within 10 days. If you want to wait longer, you can, but you’ll need to clean and scuff the surface first.

Waterborne and water-based finish materials haven’t always had the best reputation in the past, and Stewart recognizes this. “When the technology was new and introduced to the market, it took off like gangbusters. The problem is, it wasn’t very good. The single-part topcoat would crack, and wouldn’t hold up very long. The technology has advanced so much, that the finish now is really good. I’ve got one (fabric) plane that I painted seven years ago, and there are no cracks in the finish, it’s still beautiful—and it’s a waterborne polyurethane.” Aside from fewer preparation and application steps, the AFS paint system is entirely water-soluble when cleaning up. The only time you need to use a solvent or thinner is to clean out dried material. “The nice thing about these chemicals, you only need a charcoal respirator to safely use them,” Stewart adds.

Smooth As Glass When you see all of those sleek composite airplanes on the flightline, each sporting almost mirror-smooth finishes, they’re flying proof that mere mortals can and do achieve impressivelooking results. Of course, a surface free of rows of rivets and lap joints is just begging for snazzy paint job, and

the sky really is the limit. Almost. Composite construction doesn’t have many limitations, but there are a few. Depending on what type of composite material you’ve used, you may be limited to a very light base color to keep the skin temperatures within an acceptable range while sitting out, baking under the hot sun. The best authority on this is the kit manufacturer, who can guide the builder through the various implications of color selection on specific airframe material type. If you take a weekend stroll down a hangar row where airplanes are being built, you’ll probably hear some grumbling about sanding and filling interspersed with a few choice epithets. For all the advantages that composite construction has to offer, preparing the airframe for finishing requires a good amount of filling, smoothing and sanding before it’s ready for the base coat. It’s really tempting to rush this part of the process, but patience and perseverance will pay off with a shiny, reflective finish. Trust us on this one: Steps hurried or skipped in the preparation of your composite aircraft will show through stunningly well when the final coat has dried. Pinhole is another word that gets uttered a lot by composite kit builders, and not in admiration. Pinholes are left behind after the composite-molding process is completed. As the primer soaks into the weave of the cloth, the

Skip Long completes a Lancair IV project. Here he is carefully wiping down the surface before applying primer/surfacer.

result is often a small void on the surface that looks like...well...a pinhole. Left unfilled, these pinholes can wreck the appearance of an otherwise smooth painted surface. There is a plethora of products on the market designed to prime and fill, and many can be applied by several methods, including squeegee, brush, foam roller or spray. It’s very important, however, to pick a pinhole filler that is compatible with the rest of your covering system. Most major auto paint manufacturers, such as PPG, DuPont, Glasurit and Sherwin-Williams will have compatible companion filler products if you’ve decided to use automotive-type finishing products on your project. If not, a quick look at the catalogues of many aviation supply houses, such as Aircraft Spruce or Wicks Aircraft, will disclose a wide choice of preparation and covering products specifically designed for aviation applications. As with the automotive paint product lines, you can avoid all sorts of ugly compatibility issues by sticking with a single covering system (such as Polyfiber, Randolph or Loehle), and not mix primers, base coats and top or clear coats from different manufacturers. That being said, there’s always an exception. “You know what works really well as a pinhole filler?” Glasair Aviation’s Ted Setzer asked. “Spackle! No kidding. It’s light, it dries fast, it fills pinholes really well and it sands really quickly. What I do is add a bit of food coloring when I mix it up to make it stand out from the primer when I sand it down smooth. Its only job is to pro-

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vide the paint a bridge over the void, and so far, I’ve had great luck with it.”

Too Smooth? Painter Jeff Miller of Arlington, Washington, dry sands the composite surface with either 150- or 220-grit before applying the primer. After the primer dries, Miller block-sands the primer with 150-, 220- and finally 320-grit before the base coat is applied. He also smooths out the paint under the final clear coat, using 320-grit for nonmetallic and 500-grit for metallic or pearl

Believe it or not, the most effective way to lay down the first few coats of primer/surfacer is by a roller. This method helps the material sink down into those pesky pinholes. The product he’s using is Polyfiber’s UV Smooth Prime.

While the Lancair’s cowling may look like the outside of a cantaloupe now, it will be sanded completely smooth and, likely, primed and filled again before the final coat of paint goes on.

colors. “All this does is give the sealer something to bite,” Miller explains. “It’s important not to go too smooth, because the paint needs something to adhere to. With 320-grit, you’re not going to see sanding marks with most colors.” Kracon’s Ed Krass sees no real need to sand between the top and clear coats, but he does keep a piece of fine (220- or 320-grit) sandpaper handy to knock down any imperfections that might mar the smoothness of the finish. “I do keep a tack rag handy,” Krass says. “Any time you sand anything, make sure all the dust is gone before applying the next coat, and that goes for the alodine as well.” But Krass does scuff up the base coat a bit in the area to be covered by a trim color, just to provide an extra measure of adhesion. Larry Vela, of Velavision in Phoenix, is a self-confessed nut for making sure his “canvas” is as perfect as possible before he applies his artistry—and he’s found some interesting things along the way. “What people commonly call ‘fisheyes’ aren’t really fisheyes at all,” Vela says. “They have nothing to do with surface contamination. Some-

times you’ll get a random electrically charged particle coming out of the paint gun, and it will repel the paint around it on the surface.” The solution, according to Vela, is to use an alcohol-based anti-static mist (usually available from the paint supplier) between the primer and base coats, essentially neutralizing any stray charges that might affect the finish. Another common impurity that frequently and incorrectly gets attributed to improper surface preparation is a small bead of desiccant that makes it past the filter and into the paint itself. “It’s really important to make sure your air is as clean and dry as possible,” Vela says. “Unfortunately, some of the desiccant systems that dry the air can actually introduce a small bead into the air instead.” The solution is simple: a good filter after the desiccant and before the spray gun.

Ready, Set, Paint Whether you’re planning on doing your own paint job, or preparing your project to be painted by someone else, surface preparation is universally considered to be the major portion of a pleasing and long-lasting finish. “It’s not rocket science,” Krass says. “It just takes a bit of patience, some elbow grease and attention to detail.” Coming next month: Preparing fabric and wood airframes.


Contact Information AIRCRAFT FINISHING SYSTEMS

www.aircraftfinishing.com 800/653-7200 AIRCRAFT SPRUCE AND SPECIALTY

www.aircraftspruce.com 877/477-7823 JEFF MILLER INDUSTRIES

http://jeffmillerind.tripod.com 360/403-1683 KRACON AIRCRAFT REFINISHING

www.kracon.com 916/645-1614 VELAVISION

www.velavision.com 480/970-8959 WICKS AIRCRAFT SUPPLY

www.wicksaircraft.com 800/221-9425 Skip then applies the primer in strips, trying to keep the overlap consistent. 40

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