By John Wyman, EAA 462533, Chapter 266, Montreal
I think the thing that impresses me about EAA is that most everyone is a DIYer. There literally isn’t any subject in the art of building/restoring or repairing airplanes that isn’t addressed in some form by the people that run EAA. I believe this is the best of all subjects it promotes to the GA community. Their motto could easily be, “if it can be dreamed up, conceived, and/or marketed…then you’ve come to the right group of people!” I like that. Recently I took that to heart and repaired two aircraft wings. I tackled both jobs because there really wasn’t anyone else around to do it. One was a Schleicher Ka7 glider and the other was our Cessna 140. Each airplane was covered in fabric. It’s a dying art to the uninitiated, but there is a lot of information available on how to do it. Here are some details about the covering process and the obstacles involving regular “dope” painting them.
I started with the wooden glider’s wingtip, and I also did its rudder, too. After that I moved on to the Cessna. Each cover and paint improved my skill set for the next. It is generally not as hard as many think it is, but it does require oodles of patience! I kind of equate it to dry-walling … laying up the gypsum rock is not too hard, but painting it is a royal pain.
I learned several important lessons from trial and error. I used Ceconite treated with dopes as a finishing system, mainly because I had some product left over from some other jobs and also because both airplanes were covered with the same “dope” or Randolph Paint system. This was Ceconite fabric sealed with nitrates and painted with butyrates. It is a flexible paint that has a long history with fabric airplanes from when they transitioned from regular cotton to polyester. They still call it dope because the process is essentially the same (pre-polyester) except that polyester fabric (Ceconite) now shrinks when it is heated. It is an expensive system, and it has a lot of quirks that take progressive tries to get it right; most of which I’ll try to “cover” here (pun intended). There are certainly other systems worth trying, but this isn’t about those. This is about “DOPE.”
It really helps to read as much as you can about it and stick to what is said, but experiment where necessary to improve your work. Of very important note – be ultra careful with these toxic materials. The thinners and dopes rapidly soak into your skin, and their vapors burn your lungs if you’re not ultra careful with personal protection. Try to limit your time in the paint booth and get out into the fresh air in between applications. If you can feel it through your mask, then it’s time to change those organic/vapour cartridges. While doing the second (Cessna) wing, I splurged and went to Barnstormers and bought a pressure suit and spray system to have fresh air for the next job. The paints are just too dangerous to mess around with without the proper equipment. A few people I spoke to along the way reminded me of a story about one person who painted a whole airplane without protection (back in the day), who died a short while later from cancer. Dangerous, dangerous stuff!
I used these two books as guides before starting the wings.
Here are some bullet points that come to mind. Some were also covered in the books:
- If you can FEEL an imperfection on the fabric, but not necessarily see it from an arm’s length, then the anti-ultra-violet (silver butyrate dope) and subsequent colored layers of dope will show it! Before you get to this stage of applying this layer, take the time to really go over the surface and look for contaminants like dust, hairs, nicks, scratches, and anything else that “feels” questionable on the tips of your fingers. Use a “tack cloth” between applications. No exceptions!
- Make sure you’ve sharpened up a good pair of scissors. Regular ones quickly dull. I used a pair that was made in the ‘50s. The newer junk didn’t compare. I also used an X-Acto blade to scrape away small imperfections. Have a steady hand using it. If you slip, it’ll slice through the fabric like butter. One of the best tricks the books talked of was to apply fabric cement (glue) along the cut lines to shed any loose threads that’ll make for more work later. I thinned it out with just a tad of MEK (methyl ethyl ketone) to prevent it congealing into a blob at the end of a pencil thin brush. Out of all the toxins, this is probably the most dangerous. Use a mask and barrier cream on your hands. A great cream that worked for me is Rath’s pr88, which is sold in a large yellow tub. MEK is worse than acetone, but a thousand times more effective removing certain grimes and cleaning surfaces – but heck, be careful with it!
- NEVER sand bare or near-bare fabric. Make sure you have at least two coats of dope (more is better) and again, be ultra cautious sanding! Jon Goldenbaum’s book talked a lot about sanding too much. It’s very easy to do and hard to fix without recovering the ruined area.
- PINHOLES, or small volcanoes, will form on the surface when you apply the silver butyrate dope. Applying copious amounts of nitrate (the green-colored Rand-O-Proof) will reduce their chances of forming. The nitrate seals the fabric so the butyrate can adhere to it. Having too much air versus fluid from your spray gun can cause those excess air bubbles on the surface, messing up the finish. If that happens, let the dope “calm down” before you sand them out. Dope works its way into each layer beneath it forming a flexible film. You can’t cover up the mistakes, only blend the layers into one another.
- A lot can be learned by just framing up a few test pieces. Make some large and small ones to simulate the surfaces being sprayed. Wood and metal behind the fabric will simulate what you are spraying. It initially may be a day’s work building them, but they are mighty handy to have around to test for “blush,” where you’ll really start shaking your head!
“BLUSH” forms when applying dope from your spray gun. It can form on the green nitrate, silver butyrate, or colored dope. It is tough to spot. Your lighting has to be just right (ideally at a 45-degree angle to the surface), and you have to look at the area you’re spraying from all angles. Don’t hit that gun trigger after the first few passes. Wait! It takes time to dry. Only after it dries will the blush be discernible. It forms when the humidity in the air condenses into the paint when the dew point is reached at the surface of the paint where its thinner rapidly evaporates. It is milky/paste-ish and gray/white in color. That’s the water that gets trapped. It must be removed before subsequent layers of material are applied to maintain the paint’s adherence to the next layer. Retarder is used to counter this and is particularly helpful when the temperature rises. You’ll use more thinner than retarder – so buy gallons of both! In short, blush will drive you nuts unless you respect the relative humidity. Get an accurate humidity gauge and don’t spray if the conditions aren’t ideal. I can’t repeat that enough!
I learned that maximum ideal humidity was about 55%. Anything more, forget it, and anything above 52.5%, start asking yourself if you want the extra sanding work. The books I referenced go into this in great detail, but, given their wide audience with different atmospheric conditions, they shied away from any absolutes. For me, in the Northeast, near the river, 55% was an absolute maximum.
The bottom line is that if you want to get good at fabric and spraying dopes, you’ve got to do it. No amount of explanation here will have you performing miracles in the first passes of your spray gun. I learned a lot about it as I hadn’t tackled anything of this magnitude since I last helped Dad re-fabric the wings on the 140. The repairs were a bit different as I was using a paint gun instead of a roller, and I was blending the repaired areas into other people’s work. Light blushing can be “burned out” by just applying thinner and retarder to reactivate the surface and remove the blush by slowing down its evaporation. This saves you a lot of sanding. Heavier blush will still require some sanding. Ultimately, you’ve got to be bold enough to see what you can get away with for the prevailing conditions. You’ll gradually master it with each mistake – until it clicks. Be wary of trying to get it done too fast. You’ll only go backwards. Just mastering the paint gun takes a long, long time. The Aircraft Painting and Finishing book was really helpful with that. It had a whole section just on setting and holding the gun. There are a ton of terms to read up on. Do yourself a favour and re-read what you read after the mistakes. Do your homework.
Finally, if you seem lost (like I was) between choosing different equipment (compressors, guns, filters, protective gear, HVLP, etc.), call up some expert friends for advice. Don’t be SHY to ask questions even if you’re having a hard time deciphering what the books are talking about. My friends really helped me understand the whole process. If you make it to SUN ‘n FUN or EAA AirVenture Oshkosh next year, make a point of taking a fabric workshop to get the basics. Whether you use one system or another, the basics are essentially the same.
John Wyman, EAA 462533, Chapter 266 Montreal, is a passionate aviator. When he isn’t in the saddle at the airline, he can be found out at the airfield doing any number of things. He likes to fly gliders, practice aerobatics, work on airplanes, and fix stuff.