Tips on how to make minor repairs to new basecoat/clearcoat paint finishes.
As you read in Dave Jensen’s story New Promise in Paint, which appeared in our (see Aviation Maintenance, April/May 2012) issue, the aviation industry has pretty much switched from the old lead-based primers and single-stage top coats to a much more environmentally-friendly generation of basecoat/clearcoat (BC/CC) finishes.
According to the various manufacturers, these new BC/CC paints offer a variety of benefits beyond their safety: they dry faster, have a greater resistance to wear, provide a much wider range of colors and, they also offer, what promises to be a much longer life on the aircraft. And while they’re better, they’re not ‘bulletproof.’
“Even the most durable, high-quality aerospace coating system will require thorough inspections and regular maintenance,” explained Julie Voisin, product manager, Sherwin-Williams Aerospace Coatings. “Today’s latest coatings are far easier to maintain and repair. The clearcoat also makes the aircraft’s surface easier to clean than traditional single-stage coatings.”
Ms. Voisin also stated repairs to minor blemishes in the clearcoat are especially easy. “Repairs can be as simple as buffing just the clearcoat or a localized section of the basecoat section,” she said. “In addition, the shortened processing time, (up to 30-percent off traditional coating processing times) means aircraft will spend less time in the maintenance hangar.”
This Isn’t Your Father’s Oldsmobile… “Aviation is now kind of catching up to where automotive paint technology has been for over 20-years,” added Joseph Wood, North American business director, Liquid Industrial Coatings Group, Axalta Coating Systems (formerly DuPont Performance Coatings). “These new paints and coatings offer many benefits, but they also require a stricter adherence to procedures. Mainly because they have less solvents and a higher solids content.”
“We’re constantly working to enhance the application ‘robustness’ of these new finishes,” he said. “By robustness, I mean the ease of application, where if you follow a certain set of parameters you’ll get a consistent finish, cure and film properties.”
In fact, following processes and procedures is so critical to achieving the level of finish quality today’s customer demands that Embry-Riddle Aeronautical University and the Society of Protective Coatings have joined to create the industry’s first Certification for Coatings Application (see sidebar).
“We have a rule-of-thumb, that states if you are going to paint anything bigger than a dollar bill, you really need to do it in the right facility and environment to do it correctly,” Wood said. “You need to be precise in your measurement of the materials. Precise in the equipment you are using. You need the correct ventilation and air flow.”
“Remember that a lot of these new paints have modular components based on their application conditions. The size of the panel to be painted, ambient air temperature, air flow – all these kinds of things,” he said. “Really, if you’re going to paint an eight-inch square, you going to want to use a different solvent than if you’re going to paint the entire wing or airplane.”
Paint Repair 101 Wood said that today’s BC/CC coatings are a lot easier to repair than the old finishes and that you can definitely use today’s paint with the old paints. “It’s not going to crater or fish-eye massively or anything like that,” he said. “That old paint has long cured enough so that won’t be a problem.”
However, Wood stressed that you would need to follow the paint manufacturer’s published procedures and processes, including the appropriate pre-treatment steps to the letter. “I’ve seen more mistakes caused by people being in a hurry than anything,” Wood warned. “If they would just slow down a bit on the front side and make sure everything is correct before they actually mix the paint.”
Ed Mullins, technical specialist, Aerospace Coatings, PPG Aerospace stated that a good rule-of-thumb is to start with a checklist. “Best practices within the paint industry always lead back to the cleanliness of the substrate,” he said. “A good clean substrate provides a solid foundation for good paint application.”
He also suggested that technicians take full advantage of the information available to them on the Internet. “There’s much more good information available now than in past years,” he said. “It’s always best to stop when a question or concern arises and refer to the information that is available. That often leads to an answer that eliminates a costly mistake.”
And when you are doing your research, remember that, unlike a single-stage paint, you’re dealing with a BC/CC finish so you may have repair options and the Internet is a good place to search them out.
For example, if, like on your car’s finish, you see a white mark on one of the color areas, you may be only looking at damage to the clearcoat. In fact, clearcoat is very tough and there are multiple mills of it on top of the basecoat. “Repairs can be as simple as buffing the clearcoat or a localized section of the basecoat scheme,” Ms. Voisin said.
Sherwin-Williams has a really good video on repairing minor surface damage/blemishes on YouTube: (www.youtube.com/watch?v=AifGkQ87HJA) `“The only caveat on buffing is you really need to get in tune with your supplier of these types of materials,” Wood stated. “They have really changed a lot in the past few years – not only the compounds but also the technology of the pads and equipment. They’re really more designed for today’s paint coatings.”
Sometimes the clearcoat itself is damaged to the extent where you will need to respray. “You can do some of what I call ‘blending of clearcoats,’” he explained, “but I tell technicians all the time if you can get a clean panel-break and you can tape off the panel, then go ahead and respray the entire panel. You’ll get a much better repair.”
So what if you know that the damage goes down to the base color coat or even to the structure below? Again, the right repair is tied to the severity of the damage. If the scratch goes all the way to the metal or composite, it’s a totally different, and much more involved process. “A very simplified version of a repair would look like this:” Mullins explained. “Ensure the area is clean and remove all the color on the defect. From that point the repair can either be blended with a blending solvent or cleared then blended.”
“In many cases,” he added, “the area is then lightly polished to remove any overspray, being very careful not to damage the new repair.” Wood also suggested that even if you do a spot fix to the color that you clearcoat the entire panel. “That’s going to give you the highest durability and it going to wear at the same rate as the rest of the aircraft’s finish,” he said.
Ready, Aim… While a complete understanding of the exact chemistry of the primer and BC/CC is critical to achieving the high-level of quality you want, Wood also stressed that you have to use the right type of spray gun.
“The latest achievements and improvements in spray gun technologies have been tremendous,” he said. “If you think back to the ‘70’s and the old Binks model 7 syphon spray gun you’re missing a lot in what today’s sprayers can do.”
“Today probably 95-percent of repairs are done with a new gravity-feed type gun. This works so much better with the high-solids paints because you are not using energy to pull the paint up then trying to atomize it,” Wood explained. “It minimizes overspray, minimizes consumption and still gives you a great finish – especially on smaller, touch-up repairs.”
“There have also been big advancements in the paint cup itself,” he added. “Several companies now offer disposable liner cups so you don’t have to waste time and chemicals to wash the cups and it takes a lot less solvent to clean the guns.”
Interiors Need Help Too Of course with all the wear and tear that interiors suffer, sooner than later you’re going to have to do some paint touch-ups on the inside. AkzoNobel recently introduced its Dab2Fix (www.anac.com/Brochures/AkzoNobel_Aerofine_Dab2Fix.pdf ) paint application system created for quick interior paint repairs.
According to the company, the system “allows controlled application to interior surfaces, correcting surface damage in a simple and effective way. The sponge applicator ensures areas can receive a touch-up repair to maintain the overall appearance of the aircraft interior.”
StandardAero is First MRO to Complete ERAU/SSPC’s New Aerospace Coatings Application Certification As paints and their proper application requirements become more sophisticated, so must the training that aircraft painters receive to do the job properly. “Historically, learning how to paint has been primarily on-the-job type training,” explained Mike Menard, VP/GM, StardardAero’s Springfield Completions Center. “A lot of ‘tribal knowledge’ was passed along, but there was no consistent baseline or body of knowledge.”
To ensure that its customers are getting the best quality of work possible, when Menard heard about the Aerospace Coatings Application (www.sspc.org/ACAS/) certification programing being offered as a joint venture between Embry-Riddle Aeronautical University and the Society for Protective Coatings (SSPC), the StandardAero team wanted to be the first MRO to take advantage of the certification training.
“The program is great. It offers technicians a good theoretical base on which to build their craft and that translates into a better result for our customers,” Menard said. “That theoretical knowledge is often what’s missing from OJT – you know what needs to be done but you don’t know why. Knowing why is more important today than ever.”
“For example, any painter worth their salt will tell you that proper surface cleaning and preparation is critical,” he added. “But they really don’t know why. What are the things at the chemical level that make it work or not work? This certification creates a much better, more consistent foundation for our craftsmen.”
The ERAU/SSPC certification program consists of six training modules that are completed by the technician online. Menard said that it takes about six-weeks for a working painter to complete that part of the training.
“For the final exam an Embry-Riddle instructor came to the shop to see each technician put his or her knowledge into practice,” he said. “You have to prep and paint a piece of aluminum using the proper technical data sheets and you have to know why you are doing each step.”
“Going through the course doesn’t make you a painter, it just gives you the understanding of what you are doing and why you are doing it,” Menard said. “Now they know why humidity is important and why it matters what order you mix the two-part paints. They now know how each little part comes together to make a better paint job.”
Menard said that it also helps make for better moral among its employees. “It’s been a good way to challenge our painters. They use the same techniques they always have, but now they have a clear understanding of how it all works,” he said. “We’re investing in our employees’ futures. They are true craftsmen. We’re just providing them with a better foundation.”
And as we all know, when it comes to painting, the better the foundation, the better the finished product.