LOEHLE AERO COATINGS ON RV AIRCRAFT
(Applicable to any metal/composite aircraft)
More and more RV builders are using Loehle Aero Coatings when it comes time to work on the fiberglass parts, and have realized the same paint will also work on the rest of the airplane as well. Loehle Aero Coatings is formulated for metal, composite (and fabric), so all the primers, color and clear can be from the same paint process.
One reason RV builders are initially drawn to the Loehle process is that Mike Loehle has come up with a 15 minute wipe-on/wipe-off fix for pinholes called Loehle Wonder-Fil. This reduces all the filling/sanding/filling/sanding usually required to properly finish the fiberglass cowlings, wheel pants, etc. Following up with the Loehle Black Filler/UV Blocker (primer), then White Filler/UV Blocker (primer) continues this quick filling, smoothing process and brings the composite parts up to the same stage as the first coat of White Filler/UV Blocker (primer) for the aluminum. The whole airplane can have the same foundational white so whatever color is chosen can be a true, vivid color. The Loehle Aero Coatings process allows just about any color you can think of….all of them an extremely "wet-look" shiny finish.
The Loehle's have secured a huge WWII hangar at the Tullahoma, Tennessee airport for their latest venture, Loehle Aero Painting. Mike has recently painted an RV-10 for Maj. Gen. (Ret.) John Miller who is a former 3 time wing commander, including the F-117 Stealth program. Mike has agreed to share a bit of history and some technical insight on applying Loehle Aero Coatings to an RV aircraft…..
Photo A – John Miller's RV-10 before – in the rough
Photo B – John Miller's RV-10 after – finished in Loehle Aero Coatings
(John Miller - firstname.lastname@example.org.)
By Mike Loehle
I'm honored to be asked to share my painting experience with all the Van's RV aircraft builders. I'll start by giving a little history on our company, along with the reason I created my own painting process.
Photo C - Mike Loehle – President of Loehle Aircraft Corp.
Our process has actually been developed over a LONG period of time. I first started working with aircraft painting on fabric covered aircraft in the late 1970's and really started experimenting with various paint process and chemicals while working on Piper Aztecs and single engine Cessnas. I started mixing various chemicals together way back in 1981 to attempt to create a shiny, chemical resistant coating for use on my ultralights. An Oshkosh Grand Champion trophy was the result.
Over the years, I have worked with nitrates, butyrates, lacquers, vinyls, enamels, urethanes and even latex type paint chemicals. I have experience with most of the aviation paint products on the market. All work on aircraft, but some are much better and much more durable. Paint has come a long way over the years and urethanes are the most advanced paint chemistry available today. They are really industry standard now in virtually all fields…auto refinishing, custom street rods, custom motorcycles, industrial machinery and probably even the boat refinishing business. Aviation has often been the last to adopt changes in paint technology. This is a shame and the aviation consumer really doesn't get the latest improvements that come down the pike.
I started producing aircraft kits as a teenager (31 years ago) and now our crew includes three generations working with our designs and painting progress (my dad, brother, wife and two sons). Our history includes experience in many facets of aviation…general aviation, homebuilts, ultralights, and even rotorcraft. We have designed primarily replica fighter aircraft, with our most well known being the "5151" Mustang, a 3/4 scale version of the P-51 fighter. We also have a P-40, KW-909 (a ME-109/FW-190 look), Spad XIII, Fokker D-VII, SE5a, with a Spitfire in the works. Our Sport Parasol is not a warbird, but definitely a nostalgic classic. (See www.loehle.com for more details on kits).
My main goals working with paint for use on my own factory kit demonstrators were to create the most flexible coatings available and the easiest to apply. These were self-serving goals that we now are privileged to help folks with worldwide.
What I will be discussing in detail is how our process can help Van's builders with their own projects. I'll describe the basic steps I used to paint a customer's RV-10 and then I'll go into detail about each step. I have been asked by RVator's Ken Scott to make the discussion more on the technical side, as RV builders want all the technical details and that suits my style perfectly…being of German ancestry (Loehle), we too excel in the fine details! The details are numerous, but builders' knowledge varies greatly so I'm attempting to include as much information as a beginner painter might need.
In a nutshell, here's what you'll be doing:
1. Wash and prep all parts for application of Loehle Filler/UV Blocker (primer).
2. Apply Loehle Wonder-Fil on composite parts.
3. Apply Loehle Filler/UV Blocker surface primer.
4. Apply Loehle Color Top Coating.
5. Apply Loehle Clear Top Coating.
It sounds simple enough and it really is if taken one step at a time, but there are details that will make a big difference in just "painting something" or winding up with a finely crafted paint job to match the craftsmanship you've accomplished thus far.
Van's Aircraft are, as most folks know, composed of primarily sheet metal with composite parts mixed throughout. The most widely asked question for us from Van's builders is about finishing the composite parts and especially the "dreaded pinholes." I'll begin explaining our coatings and their unique properties when we finish RV glass parts, and move on to painting the metal parts as well. Loehle Aero Coatings is purposely geared for metal, composite, and fabric surfaces.
The initial step for all composite parts is to trim and fit the part to the aircraft. We don't even wash or sand the part until it is properly fitted and all holes and cutouts are finalized. Naturally, if one has to add fiberglass cloth and resin, then the applicable area should be washed and sanded per proper laminating procedures. Many builders will eat up a lot of time sanding on the blemishes in parts and actually opening up the glass surface and pinholes prior to properly fitting parts to the aircraft. This can allow dirt and grease to get into the surface of a part, only to cause paint problems later.
When the part is properly fitted, wash the part in hot (if possible), sudsy water to remove any mold releases, wax, oil and dirt from the part. This should be done before one begins sanding so as to not "spread" contaminants around and into areas as sanding takes place.
Detergents such as Simple Green and Dawn dish soap work well…just don't use a soap that has hand lotion mixed into it!
The finish on composite parts varies greatly from manufacturer to manufacturer and the amount of sanding and filling required also varies greatly. The parts we produce for our Loehle aircraft kits are normally finished in our unique Black Filler/UV Blocker surface primer, so they are much more pinhole free than bare glass parts. Like most in the industry, Van's parts are normally supplied unprimed. The parts will need to be sanded to remove the shiny finish so filler and primer will properly adhere.
Photo 1 – Lower half of RV wheel pant has been dry sanded. Upper half is still shiny before sanding.
We normally prefer to dry sand our parts so as to not introduce moisture into open pinhole areas. (Be sure to wear a good, properly fitting dust mask when sanding.) We scuff sand the surface with sandpaper grit ranging from 150 to 220. The paper we use and supply is designed for dry use and is white in color. Black wet/dry paper will clog rather quickly when dry sanding. We learned a tremendous amount about sandpaper years ago when we produced wooden Ritz propellers at our factory. Dry sanding was an obvious choice when working with wooden prop blanks so "wet wood" was never a factor. As many as 50 props a day were produced and four coats of flexible urethane were applied per prop. Each coat was sanded prior to the next, so a vast amount of sandpaper was used daily. The paper that eliminated clogs best is what we now use finishing glass parts.
What Are Pinholes?
The number one problem Van's builders complain about is pinholes. A pinhole is really just an area of a composite part that was starved for resin when the part was produced. The glass cloth is dry and will continue to soak up any liquid that enters the pinhole. Never fear though, we have a product that will actually fill them!
I'm going to describe pinholes more for those who have not yet been plagued by them. They are tiny holes in a surface that normally will repel a paint primer that is applied to an unsanded part. The reason is that a pinhole is kind of like a miniature volcano: it has a slight lip that helps repel liquid primer….actually the thinned primer will try to flow around the lip of the pinhole instead of down into it. Surface static adds to it wanting to flow around the hole.
Sanding will remove the "volcano lip" and primer will then flow down into the pinhole. The problem then is that the dry fiberglass cloth will keep on soaking up the primer until the cloth is totally saturated. This may take many coats of primer, which is very frustrating to say the least.
Loehle Wonder-Fil – The 15 Minute Solution for Pinholes
We have a special product called Loehle Wonder-Fil that is just the ticket for pinholes. Years ago we wanted to hide sanding scratches in our wooden propellers and that's actually where Wonder-Fil started in our paint process. The chemical is actually a simple paint thickener and mixes with any primer, paint or even clear coatings. It mixes so well on the spot that the sanding scratches disappeared on our clear coated propellers. When used to fill composite pinholes, it simply plugs the hole so primer will not continue to flow "forever" into the dry cloth! An old timer explained that they used to fill sinkholes in the ground with dried beans. Then when they soaked them with water, the expanded beans would plug the hole long enough for concrete to set! This is the basic principle in action with our Wonder-Fil on a composite part. The primer and the Wonder-Fil are permanently bonded together.
Photo 2 – Loehle Wonder-Fil showing pinholes in honeycomb areas on RV-10 cowling.
Photo 3 – Wonder-Fil showing pinholes in honeycomb areas on RV-10 cowling.
After sanding a part, it should be blown off with dry compressed air to remove the sanding dust. Surface Cleaner should be used prior to applying our Wonder-Fil. Our Loehle Wonder-Fil is then simply applied as if you were hand waxing a car. It is applied with a paper towel, soft cloth or applicator type sponge in a circular motion. The Wonder-Fil will be forced into the pinholes. We allow Wonder-Fil to dry (about 10 to 15 minutes) until you see a whiteish haze
Photo 4 – Whitish haze shown on upper cowling before wiping off surface with towel.
on the part's surface and then wipe off the surface residue with a clean paper towel or soft cloth, leaving the dried Wonder-Fil in the pinholes. White specks will be noticeable and you will then be amazed how many pinholes your part has!
Photo 5 – RV wheel pant nose with Black Filler/UV Blocker primer sprayed on before any Wonder-Fil was used – pinholes really show up then!
Moving On to Primer
The part is now ready for our unique Filler/UV Blocker, which is a primer/surfacer. The Filler/UV Blocker comes in either Black or White and is designed to fill or build up mil thickness quickly. We'll be using the special Black Filler/UV Blocker on composite parts and will use the White later (before spraying color).
Photo 6 – Fabric weave and honeycomb lamination clearly shows up after applying Black Filler/UV Blocker coating. Additional Black will fill in these areas.
The initial spray coat of Black Filler/UV Blocker will help fill the weave of the composite fabric and block UV radiation (sunlight) that can destroy a part's strength over time.
Our Filler/UV Blockers are formulated to spray on in one single pass of a spray gun…not several light cross coats as thinner paint coatings normally require. Remember, high build was my goal. Fabric covered aircraft will take four to eight coats of silver to block ultraviolet radiation (sun rays) that will harm the covering fabric. A 60 watt light bulb is normally held behind the sprayed fabric to check for light penetration. We pass the same test with one single slow pass of our spray gun! I know you're not dealing with fabric, but I'm just explaining how effective the protection is with just one coat.
Now I'll discuss the best feature of our Filler/UV Blockers. They dry to a semi-gloss to glossy finish and have special sanding agents in them to allow the coating to be flexible, yet not clog sandpaper. When they are dry sanded, the shine disappears
Photo 7 – Shiny finish of Black Filler/UV Blocker before sanding windshield area on RV-10.
Photo 8 – Obvious comparison of sanded and unsanded Black Filler/UV Blocker on upper half of RV-10 cowling.
Photo 9 – Black Filler/UV Blocker has built-in "guide coat" for sanding. Shiny areas show low spots and runs become very obvious.
on smooth areas and blemishes show up readily as still glossy. Car painters normally spray flat gray primer and then apply a coat of flat black spray can primer on top of the gray. When they sand the surface, low spots show up as flat black. This "cheater method" is called a guide coat. Our Filler/UV Blockers have this designed into them…the remaining shiny areas show the low spots just like the "rattle can" flat black does for car painters. Our product, however, does not introduce cheap lacquer based paints into proper urethane primers…
Even though our chemicals are possibly the most flexible in the whole paint industry, they dry quickly and will sand like "old school" lacquer primers. Special thinners and sanding agents allow this great property. Our customers love the sandability of our Filler/UV Blockers.
Seven Temperature Range Thinner Choices
While I've mentioned thinner (or reducer), let me explain our thinner formulas. All our chemicals from Filler/UV Blockers, Color Top Coats and even our Clear Coats use the same thinners. This is rather unique to painting products, especially aviation chemicals. This means that there is little chance that the chemicals will react to each other, as happens with some coating products. It has always been obvious to me that part of the "popping of paint" that folks complain about is a result of different chemicals reacting to each other. Our chemicals are all from the same chemical family.
Our thinners come in seven different temperature ranges from 50° to 115° to allow the chemicals to flow out properly and have painters achieve the exact results they want. Typical aviation coatings will usually offer two temperature range thinners and then have blush retarders to slow the drying process even further. Body shops will normally have their own heat booths to help with this as required. All our chemicals are designed to be applied in true homebuilder's workshops and be air dried. A heated booth can be used, but it is not required.
The first coat of the Black Filler/UV Blocker can be sanded in 5 to 10 minutes if our super fast drying Accelerated Thinner is used. Normally one does not need to sand that fast, but the option is there.
Please note that spray guns must be cleaned immediately with all our chemicals as they are designed to set up quickly to reduce dust and dirt from contaminating the paint. Remember most builders don't have perfect dust-free paint booths and our shop doesn't either. Our own paint shop until recent years was our dusty wooden propeller shop or even outside! This is why I created this painting process. Who would ever think you could paint a $750,000 Lancair Propjet without a perfect dust-free paint booth and achieve a mirror finish?!?
Photo 10 – Lancair IV Propjet in typical low cost (plastic) homemade spray booth inside our huge WWII hangar – finish shine is obvious.
Well, enough special chemical details for now. Let's go ahead and get ready to spray the initial coat.
Suit Up for Safety
When spraying any chemicals, we always recommend you use proper protection – skin, lung and eye protection. Good coveralls and gloves are standard for all painters. A proper charcoal cartridge type respirator is the minimum one should use when spraying paint. If you have access to a fresh air respirator, that is even better. Most painters in industry – industrial, automotive and aviation – prefer the ease of use of charcoal respirators. Fresh air has been a real hard sell to painters because they are expensive and somewhat cumbersome. The price has come down a lot in the last few years to under $500 for a unit with mask and hood, so we put them on our list for those who want them. Charcoal respirators are legal in automotive spray booths using catalyzed urethane paints and this is what we use as a minimum ourselves. You should cover your head and even eyes. Many professionals do not wear eye protection, but they should. Goggles with tear-off plastic sheets are available.
Getting Ready to Spray
Applying the first spray coat of Black Filler/UV Blocker is rather easy. For our thick Black or White Filler/UV Blockers, we use spray guns with tips sizes of 1.7 to 1.8. These are referred to generally as primer guns. Before spraying, blow off the part to be sprayed with clean compressed air. We use a clean latex glove on one hand as the air is applied from the blow nozzle with the other hand. The gloved hand aids in breaking dust particles away from the part surface. It simply cuts the surface tension and static and the application of air blows the particles away. Be careful to not get the air so close to the surface that it blows out the special Wonder-Fil. Also, I do not use surface cleaner at this point because it also will remove the Wonder-Fil. A tack rag can be used instead of the latex glove – most professional painters use the tack rag method.
The mixing ratio for our Black and White Filler/UV Blockers is 4:1:1 – 4 parts Black or White, 1 part Universal Thinner, and 1 part Filler/UV Blocker Catalyst. Two methods can be used to measure the mixing ratios. We use marked, graduated mixing cups that we supply for large parts. For small parts, I use small mixing ladles. The ladle method is really accurate and allows you to not waste chemicals. There is a short learning curve to figure amounts needed for various part sizes, but you can pick it up quickly.
The air pressure used to apply the Filler/UV Blocker is 6 to 9 psi at the cap for HVLP guns and 25 to 45 psi for HVLP and siphon feed guns. The more air used, the better liquid chemicals are "atomized" or busted up into fine particles. When you hear of "orange peel" painted surfaces, generally it starts out as air pressure being too low. Modern HVLP spray guns are notorious for this. Everyone has been told HVLP will greatly reduce overspray and they can, but overspray is finely atomized paint particles, which produces smoothly painted surfaces! (I have a separate article on our website at www.loehle.com that discusses spray gun tips.)
Most novice painters can't even measure the "at the cap" measurement. Also, the 25 to 45 psi is at the incoming end of the gun and with the trigger pulled – not the gun at rest.
The next way that orange peel is reduced is with the thinner. Extra thinner is one way some folks get paints to flow out nicely, but you lose the ability to rapidly cover in as few coats as possible. Older style and cheaper paints use additional thinner in their products. Thick high build chemicals and pigments cost more money.
We prefer to change the temperature range of the Universal Thinners we add and this step changes how fast the paint will "flash off." The longer it takes to flash off, the more time the paint droplets will have to flow out evenly. Too much added thinner or too slow a flash rate thinner will help create runs. We have purposely created our Universal Thinner system to aid in giving a painter the best of all worlds.
Spraying primer is a great place to learn how to paint, so don't lose sleep over all the technical things I've thrown out so far. The Loehle system was set up for novice painters as well as pros. We've invested 25+ years to aid folks to learn to paint their own project and get the "wow" factor from their buddies!
I recommend that the first coat be applied by testing the spray gun on a clean piece of cardboard or masking paper taped to the wall. This is standard shop procedure for most painters.
I like the spray fan to be slightly under the widest fan pattern. Remember that when you narrow down the fan spray pattern, paint is being applied to a tighter area and runs can quickly show up. In primer especially, you just quickly sand them away. A few runs will actually help you fall in love with our chemicals' sanding properties---they sand well and all runs are visible immediately because of our flat vs. shiny built-in guide coat (see Photo 9). With a little practice you'll get the hang of it.
Spraying the First Coat of Black Filler/UV Blocker
After setting up your spray gun, spray one full coat of the Black onto the part surface. Move the gun slow enough to completely cover as you go. Too fast and the paint will be thin. Go way too slow and, you guessed it …runs. Just a little practice and you'll see.
Some painters will want to apply two or more thinner coats instead of one thick one. That's ok and all our paints can be applied with many various techniques. What I'm trying to show you with the one coat method is the coverage and this allows you to get used to spraying. The Black sprayed over a composite part easily shows you exactly where you've painted and where you've missed. The dark black is dramatic.
Allow the part to dry well before you start to sand it. This time can vary from 5 minutes to an hour or so depending on the temperature of your shop and which thinner you chose. Setting the part into direct sunlight will speed up the drying. Our Filler/UV Blockers dry very fast compared to most paints anyway. When dry sanding, if the white dry sandpaper gums up, the primer is still a little "too green."
Photo 11 – Smoothly sanded upper cabin area of RV-10.
Spray Gun Cleanup
I pour a small amount of thinner into the gun and cover up the top vent hole while I lightly shake the gun to clean the inside of the cup, by spraying the gun until only the thinner is being sprayed out the nozzle. (Note: This may be illegal for EPA reasons in some states.)
Be sure to clean your spray gun out completely. We use very "hot" lacquer thinner for this purpose. Do not use the more expensive Universal Thinner for this. The "hot" cleanup lacquer thinner is much cheaper and does a much better job. (Note: Just be sure to introduce the Universal Thinner back into your gun's system before spraying your next coat ---you don't want lacquer thinner to mix in with your next step or you'll possibly have a problem called "fisheye".
I personally use a plastic spray bottle to wash my gun down. The spray helps remove the thick paints quicker and less thinner is used. I wash and spray the gun parts over a plastic bowl to catch the thinner run-off.
I sand the part with dry 150 grit open coat sandpaper to see how many blemishes and pinholes are left. Van's parts will have a good bit. I use a 6" orbital "DA" sander normally, but the parts can be sanded by hand equally well – it's just slower. Remember to use a dust mask and think ahead about where all the sanding dust will go. A small bench outside is handy and keeps your spray area cleaner, and helps keep peace at home!
The blems will show up immediately and you'll fully understand why these chemicals were created. Missed pinholes can have more Wonder-Fil applied to them and large areas can have filler added to them. Epoxy fillers or polyester types are all ok. The epoxies will slow the process of filling and sanding down generally a whole day. I know there are lots of opinions about epoxy vs. polyesters and I won't try to convert you either way…I do know that from my experience the polyesters work well and are much faster to sand. Some argue that epoxies don't shrink and polyesters do. I do know that your Van's epoxy laminated cowlings will show little or no cloth weave on the surface when they are new. A year or so later, the epoxy will pull down and a slight cloth weave will be noticeable. Some RV builders will even leave their unprimed parts in the sun in an attempt to allow the shrinkage to minimize. Well, back to the fillers…I think they all shrink somewhat and polyester possibly more, but I don't see the use of epoxy type filler in the automobile field and even in the $200,000 to $300,000 street rods and custom motorcycles. I use mainly polyester fillers and might choose epoxies when working the glass work on top of an RV-10. This would primarily be for large fill areas. Small blems in wheel pants and cowling seem to be fine with polyester.
Photo 12 – Black Filler/UV Blocker mixed with microballoons to create a special paste to fill blemishes on front of wheel pant and strut fairings.
Photo 13 – Black Filler/UV Blocker microballoon paste to fill blemishes on oil access doors on cowling.
Photo 14 – More microballoon filling.
We mix microballoons directly into our Filler/UV Blockers and putty these into blemishes routinely. This eliminates any "foreign" fillers to the primed area. This will require a longer dry-to-sand time than a sprayed on chemical. Our Accelerated Thinner should be used to help speed up the drying process. Enough on that opinionated topic.
Once you have the blems filled, you can apply another Black coat and repeat the process. I do not wipe the sanded part with surface cleaner before reapplying the next Black coat unless the part has sat around a day or two or if friends have visited the shop…smooth sanded parts seem to attract oily fingers! Just wipe down the surface with surface cleaner then. Remember that you will remove any Wonder-Fil you've just applied if you do. Also proper technique for using surface cleaner is to use a lint free shop towel or virgin cotton rag. Wipe the surface, turning the rag until the surface of the part is dry. Do not leave the surface wet. The purpose is to have the cleaner move the dust and oil to the rag.
Also, I use only "known" surface cleaners, and ours is listed on our product list. Some recommend that anything that smells like Coleman fuel is ok---not for me. Enough problems arise when painting an aircraft without creating one with unknown chemicals.
One note on our Wonder-Fil: We use it to fill open pinholes primarily. It will fill other areas, but our thick Filler/UV Blocker really is what works best. Previously filled pinholes may be visible as the previously applied Black will soak down into the hole and sometimes leaves a slight depression. The next Filler/UV Blocker coat will level them out quickly. Wonder-Fil can be used at any step of painting—all the way through clear coat. Remember it turns whatever color you are spraying – even clear. You know it is mixing with the paint when you see it go from white to invisible!
Repeat the priming process until you have the totally smooth, flat looking sanded part. It doesn't get better than that.
Many builders that use automotive paints normally use flat looking gray primers and the surfaces will "look great" until shiny paint or clears are added. I do not use typical base coat/clear coat for similar reasons. The color base coat can look perfect after it dries to a dull, flat look but blemishes and runs can show up when the clear coating is applied. What I'm driving at is the initial priming steps never fully removed the blemishes as flat gray finishes help hide them. Our shiny vs. flat sanded Filler/UV Blockers let you work them out in the earliest stages of the painting process.
All of what I've written to this point may seem overwhelming, but it's not…anyone that wants to paint can paint. The details I covered for the initial Black Filler/UV Blocker will apply to all the rest of the painting process. The basic fundamentals are the same – air pressures, dry times and mixing ratios can vary, but overall after your first smooth composite part you'll be on your way to being a painter!
Application of White Filler/UV Blocker
Continuing on with the composite part described previously, the smoothly sanded part can now have the final priming coat of our White Filler/UV Blocker applied. It is mixed the same way. Spray it on with our single coat method or several lighter coats…the goal is to cover the Black with White so color coats to follow will look top notch and vivid. Most bright colors will really jump out or "pop" when you apply them over a white base.
Photo 15 – White Filler/UV Blocker sprayed over smoothly sanded Black coats.
Photo 16 – White Filler/UV Blocker applied to all metal wing of RV-10.
Gray type primers can be harder to cover with some colors. Later "tiger stripes" may show up in varying light sources. Simply put, the darker gray may show up through the paints. Most aircraft are largely white, so we choose to use white pigments in our second stage Filler/UV Blocker (primer).
If your parts or even your plane is a dark color, you can simply use our Black Filler/UV Blocker under the dark color coat. I lay down the White all over before painting most colors.
After sanding the White with 400 grit dry sandpaper, the part is ready for color. If you want to wet sand as some do at this stage, that's perfectly fine as you hopefully have all the areas sealed from water by now. 320 to 400 grit is good for the wet sanding process.
A maroon or gray Scotchbrite type nylon pad is used right before color is applied to remove all shiny areas. This helps assure proper paint adhesion. I've done numerous test panels over the years without scuff sanding prior to the next coat of paint with very little peeling problems but you should scuff any surface being painted. This applies to our paints or any other brands.
A note on this with other brands… I have a sneaking suspicion when one sees clear coating peeling off of cars and planes, it's because of the fact that the surface was not scuffed prior to clear application. Base coat/clear coats normally recommend that you not scuff them prior to clear coating and the results may be what we see way too often. Even base coat that has been previously applied several days or weeks before generally is said to need sanding and even repainting before adding on the clear coats. I know there are many opinions on the use of base coat/clear coats, but in 20+ years, peeling paint has never been a problem for me. (Ask my wife about my paint on an "unscuffed" coffee mug sometime!)
Painting Metal Surfaces
Now let me discuss the application of our Filler/UV Blockers (primer/surfacers) on metal parts of a Van's RV. Normally I apply only our White Filler/UV Blocker as there is not a need to use the Black. We're not trying to find composite blemishes or even block UV rays for this step…only apply the most flexible, high quality primer we can produce. One may question why we want flexible on the metal parts also. All materials will expand and contract with heat and metal can really expand. I first noticed the peeling of paint as a teenage line boy. The FBO I grew up at had 20+ Cessna 150s for rent and when you fuel that many planes of the same type, you can start to see first-hand where paint problems first start. The paint breakdown points I always remember were on top of the wings where the sheet metal panels were joined. The paint seemed to be so brittle in these areas that as the panels expanded and contracted slightly, the paint would split and then start to peel. The Loehle Ultra-Flex flexible technology is designed to delay the effects of the paint drying and becoming brittle. All paints eventually seem to become more brittle as a lot of time passes, but with proper flexible additives the paints last longer (which, of course, it the goal).
Photo 17 – Black Filler/UV Blocker used to achieve smooth blends of composite areas to metal area.
Areas on RV's that blend composite parts to metal (such as mentioned previously on the RV-10) will have Black Filler/UV Blocker used in those areas. They will be coated with White Filler/UV Blocker to blend into the White Filler/UV Blocker used on the sheet metal. Remember, the Black just helps you make glass areas completely smooth by showing you the blemishes. The White has the same finishing and sanding and shiny vs. flat properties…it's just much easier to see how to do the work in the Black color.
Aluminum Prep – Clean and Sand First
Well, before you apply any White or Black Filler/UV Blocker to the sheet metal, you will need to prep the aluminum as most Van's builders know. I think entire internet band width has been used up on this subject over the years! I won't get into all the varied options, I'll just tell you how we do it. Our methods utilize two processes. The first is the industry standard one of aluminum etching followed by using Alodine. The second method is the use of Pre-Kote. Both methods are great in my book but I prefer Pre-Kote because it seems to be easier and is environmentally friendly.
To start with, you will need to thoroughly scrub the surface you are working on with an alkaline detergent (such as Dawn).
Photo 18 – Metal surfaces need to be properly scuff sanded. Right side shows 400 grit sanding and left side shows the initial use of an abrasive pad.
Abrasive pads should be used with the detergent to assure the surface is completely clean. This will also scuff the surface and allow future chemicals to work properly. All surface areas need to be scuffed with these abrasive pads. Rinse with fresh water the whole time you are cleaning the surface. Do not allow the detergent to dry on the surface.
If you have rough areas, the can be sanded lightly with 220 to 400 grit sandpaper. Areas on an RV that require some of this is some slight protruding rivet heads. One must naturally use common sense and not sand away a bunch of metal thickness or generally even remove the Alclad (pure aluminum) layer on the metal. 220 grit sandpaper is about as coarse as we would ever go.
The shiny surface of sheet metal will need to be scuffed or your paint is probably not going to stay on very long…not to mention that the metal prep treatment will not work. The rule of thumb is if water beads up on the surface of the metal, it's not ready for metal treatment or paint. My favorite tool to accomplish this is the red/maroon Scotchbrite hand pad. This is usually done with a lot of elbow grease with soap and water. By the time you read this article, I hope to offer the pads for use on an air operated "DA". This will be faster and will help you and me to still have elbows in our later years!
Some builders will use square electric sanders with Scotchbrite pads on them. The surface area where you are working is best kept wet during the process. One needs to keep this in mind if you elect to use any sander that is not air operated. Be very careful with electric sanders of any type around water. Use common sense. The surfaces should be thoroughly cleaned and rinsed with clean, hot water (if possible).
Aluminum Etching - Application
People complain about having to spend the time to properly treat aluminum. Compared to the entire process of building and/or painting an aircraft, the actual work is rather trivial compared to the overall picture. The effort will always be worth it in the years to come…and the paint that will be applied will have a better chance of bonding and not popping off in the future.
We would never consider not properly treating the surfaces of an all sheet metal aircraft. As stated previously, the metal surfaces are structural and all practical steps should be taken to prevent corrosion, and etching and Alodine or Pre-Kote are currently the industry standards for individuals to accomplish this.
After the entire surface is thoroughly scuffed and cleaned, the surface needs to have a chemical etching process applied to it. Our Aluminum Etch is the chemical to be used with our Loehle Aero Coatings. The chemical is diluted with water before it is applied. For heavily oxidized areas, mix the Aluminum Etch with a 1:2 ratio…one part chemical and two parts water. For lightly oxidized and other surface areas, use the Aluminum Etch in a 1:4 ratio…one part chemical and four parts water. Do not mix the solution in a metal container. Mix and store the chemical in a plastic container only. Also do not use the solution below 60° F.
The Aluminum Etch is a phosphoric acid based cleaner and brightener, so one will need to protect any areas that are not to be treated with plastic (polyethylene) sheeting and masking tape. Any seams in the sheet metal that might have excess chemical solution "wick" or enter into them and not easily rinsed, should be taped up while one is working with large amounts of the etching solution. The areas that one elects to tape up with masking tape can then be treated as a localized area. This is normally not a real problem if one uses common sense around seams. Most seams that allow the etching solution to enter can also be rinsed out right after, if one pays attention. The solution must be rinsed off before it dries.
The procedure for applying the solution of Aluminum Etch is rather simple, but must be done correctly.
Photo 19 – Scuffing surfaces with abrasive pad. This is typical of initial scrubbing with detergent and when applying aluminum etch, Alodine or Pre-Kote. Surface must not bead up water or it's not scuff sanded enough
Apply the diluted solution with a brush, abrasive pad or sponge. Wear rubber gloves, protective clothing and eye protection. Keep the surface wet with the solution for 2 to 3 minutes and then rinse the solution off with clean water. If the solution is allowed to dry on the surface, one must reapply the solution and repeat the 2 to 3 minute period and rinse it off while it is wet. The most common reason one has to repeat the process is that one tries to work too large of an area and accidentally allows the solution to dry.
The surface must have been scuffed previously with the abrasive pad to allow the Aluminum Etch solution to remain wet on the surface for the 2 to 3 minutes. The solution should not bead up on the surface, or the scuffing procedure was not done properly. The solution must lay like a sheet (film) over the entire surface one is working or the etching process will not work properly.
Some individuals advise that you can scuff up the surface to begin with while you are etching the aluminum. We feel that it is best to actually scuff up the surface while you are cleaning it with the detergent and abrasive pad. If you leave the scuffing to be accomplished at the same time you are etching the surface, one would think that you would be weakening or at least contaminating the etching solution…
While the Aluminum Etch solution is still wet, rinse it off with clean water. The water should not bead up or the surface was once again not scuffed properly. If you did miss an area, it will probably show up here again. None of this process is complicated, but you need to work areas small enough to prevent drying of the etching solution.
If you want to stop here with the process, the surface needs to be dried completely with filtered, high pressure, compressed air. Blow out any and all seams very well.
We first used an Alodine treatment way back in 1977. The process has not really changed since then. The process is very similar to metal etching. It is not any harder than the previous process. It is well worth the effort and we prefer to use Alodine that colors the aluminum a golden (amber) color. The color really helps you know you have the areas properly treated.
The Alodine is not diluted, but applied full strength. If you elect to apply Alodine, you should apply it while the surface is still wet…right after the Aluminum Etch process is best. You could apply it up to 4 hours after the Aluminum Etch, but again, right after is best.
Apply the Alodine with a brush, abrasive pad or sponge. Wear rubber gloves, protective clothing and eye protection. Keep the surface wet with the solution for at least 3 minutes or the time specified by the manufacturer. Then rinse the solution off with clean water. You should see a nice, uniform golden color. Some aluminum will not show the yellow cast very much. Blow everything dry as stated previously with compressed air.
The structure is now ready for the application of White Filler/UV Blocker. Handle the surface as carefully as possible and try not to get oily fingerprints, etc., on the treated surfaces.
We like to apply the surface primer as soon as possible. The same day is best.
Pre-Kote works similarly…but is a one-step process instead of a two-step. This newer method is approved by several airlines and military applications and is easier to use.
Most aircraft have some steel parts on them and we have a Steel Etch solution that can be used. We can also supply special etching primers and/or epoxies to go under our Filler/UV Blocker primers if customers want. Urethane surfacers (primers) are replacing zinc and epoxy coatings throughout industry, but the aviation community is sometimes slow to accept changes.
Most Van's parts are new and rust-free so we use a simpler method for these. I generally will sand the part as required and if bare metal is showing, I will simply apply a light coat of zinc chromate to the exposed areas. Zinc rich etching primer also works well followed up with our White Filler/UV Blocker primer. With light sanding with 320 to 400 grit sandpaper and you're ready to apply our flexible Color Top Coats.
I will generally sand the White Filler/UV Blocker lightly with 400 grit sandpaper and follow it up with a maroon or gray Scotchbrite type pad to remove shiny areas. This light scuffing allows you to do a final inspection of areas before you go to the color stage. Any problems can be sanded and that particular area re-primed with White as needed. There is not a reason to apply a new coat of White over the good surface areas. Simply lightly sand to blend the touch-up area into the other area and you're ready for color.
Our Color Top Coat is then applied over the sanded White Filler/UV Blocker. The color choices we can provide are almost unlimited. Our standard colors are simply matches of the well known colors that have been used in aviation for years. Special colors, such as metallics, are available. The easiest way for us to provide them presently is to have folks supply us with a chip of color they like or a paint number from another brand of paint. We can supply virtually any modern colors – even the hot ones on street rods, etc. All our Color Top Coats are fuel and chemical resistant.
I use an HVLP spray gun with a 1.4 to 1.5 size tip for spraying on our Color Top Coats. The mixing ratio is 8:4:1:1. This is 8 parts color, 4 parts Universal Thinner, 1 part Color Top Coat Catalyst and 1 part Flexible Additive. Air supply is between 8 to10 psi at the cap for HVLP guns and 45 to 60 psi for HVLP and siphon feed guns.
Our Black and White Filler/UV Blocker and our Clear Top Coats do not require the addition of Flexible Additive to them as it is already factory mixed in for you. The Color, however, requires the flex to be added when it is time to spray. The almost unlimited colors we can supply would become very limited if we tried to pre-package the flex into them. The reason is colors are mixed using gram scales and various toners to achieve the colors, metallics and even pearls. The formulas are pretty much available to us worldwide to achieve the exact color in our paint, but we have to rely on industry standards to offer the vast selection. The weight of our Flexible Additive would destroy all the present gram scale formulas and mixing ratios. I hope that's not too confusing and I normally don't even try to explain it to kit builders…but I realize Van's builders want to know and understand the fine details.
The spraying technique is different for applying the Color Top Coat. Colors, ours included, are thinner than surface primers. They will run easier so we apply them more like "older type" chemicals…we spray on a "tack coat" and allow it to tack up. This means we want it to be able to be touched lightly without getting onto one's finger. This can be checked by touching an area that has been masked up. This tack coat is essential when spraying metallics, as the flakes will move around if you don't use tack coats. Also, a good tack coat will help prevent paint from bleeding under masking tape. This is especially helpful when you apply additional trim stripes, flames, and other type artwork.
I like to follow up the tack coat with a single heavier coat in the opposite direction. I prefer to allow this coat to flash off somewhat before I apply a third coat. Some colors get by with a tack coat and a single full wet coat…others require more. Some metallics are best put on with many lighter coats. Our customers that have shot numerous brands of paint say we generally cover better than ones they've used before. One 25+ year commercial painter told me my mix was the only gray he ever applied in one wet coat! We use some of the best pigments available and don't water (thin) them down like some economy type paints. The ingredients in paints are a worldwide commodity and generally if they're cheaper, there's a reason. We specify only the best we can get for our paints. A car may be painted and be sold to a new owner in a year or two….before the paint breaks down. Our paints may be on an airplane that may stay in one's family for 25+ years. That's my goal for Loehle Aero Coatings.
Photo 20 – RV-10 flap with White Color Top Coat applied over White Filler/UV Blocker.
The Color Top Coat will take longer to dry compared to our Filler/UV Blockers and Clear Top Coats. One should try to keep down dust, etc., as best as possible during this process. We do provide customers with faster thinners for special circumstances, but we generally apply our colors and wait until the next day to sand or scuff them. Some folks like the quicker drying feature of base coats, but I find they are nowhere near as durable as our catalyzed Color Top Coats. Longevity and durability is what our paints are all about.
When applying additional trim colors to a previously painted color, you really want the paint dry enough to scuff sand and not leave tape marks. Most of the time the next day is fine. Also, tape marks will disappear by lightly sanding before clear coating.
One note, our colors can be applied and will dry so shiny that I have trouble convincing some builders to apply the clear coat. Some say they are amazed at the shine. I say wait until you see the clear!
Since our colors are rather durable, it is rather easy to sand out dust or other blemishes prior to clear coating. We even have a cool tool that will shave off runs…and you guessed it—we call it a Run Shaver. We're always trying to make the job easier, faster and more user friendly.
I lightly sand the shine off of our Color Top Coat to get it well prepped for the final Clear Top Coat. I will wet or dry sand lightly and follow it up with a gray Scotchbrite pad. I am particularly easy with wet sanding, especially on the very edges of sheet metal joints. It's easy to remove edges on RV wings when sanding them. I will normally use the nylon pad to do this.
If something is accidentally sanded down to White Filler/UV Blocker, I use a touch-up air brush to lightly blend in the Color Coat. It works well and the paint droplets are usually rather fine. Sometimes the brand of airbrush will require the use of more thinner and numerous coats to blend the color exactly. It's easy though.
Photo 21 – Blue plastic finishing tape applied to windshield for perfect paint line. Good quality paper tape is butted next to the plastic tape.
Let me discuss the use of masking tapes also. I am a firm believer in using only modern plastic masking tapes. I use either blue or light green fine line plastic tapes. Good quality paper tapes are also used to butt up against plastic tapes.
Photo 22 – Masking tapes and high quality "no bleed" (coated) masking papers make the paint job nearly perfect.
Modern urethane paints will generally take longer to flash off or dry than old lacquer type paints or base coats. They will creep under most paper tapes – even the best (expensive) brands. The plastic tapes were designed for this purpose. They will normally pull off rather cleanly after the paint is dry. I do not pull tapes while things are still wet…some painters do, but I seem to always get little paint strings or hairs or cobwebs everywhere when I try it.
I take my time when pulling masking tapes and even have a pointed Exacto razor blade in one hand in case I run into excess paint buildup over a tape edge. It's amazing that the paint can become so strong…starts to become like the actual tape with thickness buildup.
I will lightly sand the edges of trim stripes with 400 to 600 grit sandpaper to remove the slightly raised edges left by the use of masking tapes. The thin light green type plastic tape is not as thick as the blue type, but one must be careful using it as it will stretch easily. When it stretches, it will narrow down and mess up good straight paint lines. The thin green is used for things like flames, and such on street rod and motorcycles. Most airplane painting like an RV is best with the more durable, thicker blue tape.
Once all is painted in color and scuff sanded, the final clear is next.
Clear Top Coat
If you don't even apply Clear Top Coat to our colors, they are still durable, shiny and chemical resistant. I designed my method of clear top coating back in 1988 to be applied over vinyl graphics (decals) and to seal in colored paints.
Photo 23 – All labor intensive painted trim work is sealed in a protective Clear Top Coat.
When you scratch our clears by dropping a wrench or something on them, the possibly exposed color is just as durable as the clear top coat! My clear coat experience on vinyl graphics was early enough that the vinyl companies said do not even try to apply clear over them. Well, it worked great and it's pretty well industry standard now!
The Loehle Clear Top Coat is formulated to be applied in as few coats as possible. I actually refused to consider bringing my paint system to the consumer market in the early days. The clears that I could get were thin and would run very easily. It used to make even me frustrated when all looked good, then a huge run would show up. My clear is formulated to be as flexible as any produced and also as thick as any I know of anywhere. This "thick" property allows one to apply less coats to get proper mil thickness. It is also designed to flash faster than usual, so that dirt and bugs will be less apt to be trapped.
Photo 24 – High gloss unpolished shine of Clear Top Coat applied to upper RV-10 cowling.
Some typical automotive clears will stay tacky for a very long time before they flash off and become dust free. If you have a dust free paint booth that you can close up and walk away from, a slow setting clear is ok. This type of clear can easily run off onto the floor when too much is applied by us novice painters—myself included.
A painter can extend the time it takes to flash off with our coatings simply by going to a slower setting (warmer) thinner. If normal temperature calls for a T-3 (70 to 85°) Universal Thinner, a T-4 or T-5 can be used. Some painters like to put on a good bit of clear and let the slower setting catalyst or thinners to flow out the paint droplets to reduce orange peel. I generally find that a slight orange peel (like most factory painted cars) is better than runs! A little practice and you'll be fine with our Clear Top Coat. Any dirt, dust, runs and even orange peel can be removed simply by sanding and buffing with various grades of sandpaper and polishing compounds. It's pretty easy to do with our clear coatings, but once you see how well it works, you'll probably want your whole RV buffed!
Buffing, If Desired
I'll quickly mention the buffing/polishing process and can go into extra details for folks later if requested. I like to sand our Clear Top Coat first with 800 grit sandpaper. It works ok dry sanded, but eventually small dust buildups form on the paper and cause scratches …not all that great. Wet sanding is better. We are currently working to supply a sanding system that will machine sand using wet type paper. If we can, the process will become really fast to sand and polish a whole aircraft.
Photo 25 – Final buffing of Lancair IV Propjet fuselage…shiny curves galore!
I recently sanded and polished an entire Lancair fuselage in one day.
I step sand first with 800 grit, then 1000, followed with 1200 grit. The final step in sanding is a wet sanding process on a 6" "DA" machine sander using 3000 grit paper. The clear will shine to a semi-gloss when the 3000 is finished.
The machine polish step is done with a 7" buffer running about 2000 to 2500 rpm with a foam buffing pad. A special cutting compound is then applied with the buffer. The clear will actually slightly soften and turn to mirror like glass. It's pretty amazing!
I had decided early on that I only wanted the best clear coat that chemists could produce for final buffing/polishing, even though most airplanes are not buffed. I tried to make it good enough for the "very picky" street rod folks, and knew if I did that I would have the very best for aircraft. Maybe we'll supply to the street rodders in the future….
A good quality wax is applied after the paint cures out. I will be offering my own whole system for sanding and buffing in the near future. I've tried a good many products and methods to date and I've even been able to show some body shop folks some new methods…and they buff almost daily.
The last item I want to touch on is the "saving of money" in finishing an aircraft. I have heard builders say for years that they really don't care how the plane looks, they just want it airworthy. This is a mistake in simple attitude. The truth is they would like a nice looking plane, but are either not sure how to do it or they want to save money here at the end of their project. What they will see every time they walk into their hangar is a rough looking or dull finished airplane. Other pilots will also express their opinions openly and it will start to hurt one's pride. And the honest truth is---if the finish is poor, people will also wonder about the rest of the workmanship.
The complaints I hear often when professional shops do the painting is that the cost was reasonable, but the customer spent additional weeks removing slight overspray and runs. Saving money becomes relative at this point. I have also seen professional shops offer low rates only to skimp on surface prep and the amount of primer and paint used on RVs. This leads to paint popping off numerous rivet heads, etc.
Most pilots' airplane is really their "pride and joy". Why would you want to skip on the finish? If this were your car or boat, would you paint it with house paint or any other cheap paint? I doubt it. If you really want to save money, just don't put in the "latest electronic gizmo" that will be outdated long before you're tired of your plane. Also, if you go to sell your plane, shiny ones sell quickly and for more money. Enough said…
Invitation – Starter Kit
Well readers, I could probably go on forever on my passion for my chemicals and why the whole process was created. I've tried not to make this a sales pitch at all and I truly hope you enjoy the tips and pointers shared in this article. The products I've mentioned and that are on our product list (from tapes, tack rags, sandpaper, etc.) are tested and used in our own shop…
I'll invite you to try our system for yourself. I'm sure you'll see what it can do for you on your own RV. The complaint I've heard the most from our customers is why didn't we offer it for their previous plane?! I couldn't ask for a better complaint!
If you want the shiniest, wettest-looking, most up-to-date system on the market today, with our Loehle Ultra-Flex technology, try our process first hand….quart starter kits are available. Just call (931-857-3419) or email (email@example.com) and Sandy Loehle will help you with your questions, a starter kit, a free quote for materials (or us painting your plane), or just literature to study for now.