By Pete Peterson • Originally published in Stunt News, January/February 2009
Editor’s note: This article was originally published in Stunt News and has been reformatted for digital readability. Original terminology, measurements, and technical details have been preserved where possible.
Bob Hunt asked if I would write an article on transparent finishes and the methods and products I use. Stay with me if I repeat things or ramble a bit. Some of this is worth repeating, the rambling is just me being me. I hope our esteemed editor can make some continuity appear on these pages.
Where to start? For some if not all, this will be “old hat” and repetitive. I hope each of you will get something out of it. I can only vouch for the methods and products I use. Other combinations work, but either I have not used them or tried them and decided not to continue. Here we go…
The author’s new Jamison Special is covered with polyester tissue. He used House Of Kolor Lime Gold, Sig Metaic Maroon and Jet Black trim colors. The total weight of the finish from bare wood is 3.78 ounces.
Transparent finishes by their name show everything: good craftsmanship and bad. Accurate, clean, tight fitting wood joints are a must, as is the choice of wood. Try to pick wood that will be seen on the surface of the model that contains no blemishes, dark spots, or chips and dents that will need to be filled. Save your blemished wood to use on internal structure that won’t show.
The use of most fillers, putties, and patches are pretty much a no-no as they also will show through a transparent finish. The filler that I use is zinc stearate. It is compatible with dope and mixes easily. I mix it with the reducer first and then add the dope. It is extremely light and dries clear. It is available from Aero Products. (See the sources column at the end of this article.)
I want to discuss a little more on wood joints. I have been using a great method to hide wood glue joints on the surface areas for some time now. I could not remember where I picked it up until I was doing some research for this article. I will write more on that a bit later. When gluing top blocks, nose blocks, carved or molded wingtips to wings, bottom blocks or any other joint that will show on the surface, try the following.
The glue should be a 50/50 mix of a sandable aliphatic resin such as Sig Bond or original Titebond and water. Using a cotton swab and water, wet both surfaces to be joined. Apply a thin even coat of the glue mixture to both surfaces and join. Wipe off as much excess as possible using a dampened paper towel and tape or clamp the parts together tightly until the glue has dried. I usually wait overnight depending on temperature and humidity.
With the swelling of the wood and the sandability of the glue the joint will be almost invisible after sanding. Aliphatic resin is not reactive with dope and will remain smooth as the model ages.
Another use for water: Dings, dents, and small chips can be raised by wetting the dinged area with a wet cotton swab. The balsa will swell and the area can be sanded smooth when dry. Deeper dents and bigger dings may require you to use a MonoKote heat gun to help promote the swelling of the balsa. It’s amazing how well this works, so if you make a big boo-boo, don’t panic until you try fixing the damaged area using this method.
If you feel that a putty-type filler is needed, try the lightweight vinyl spackle from home improvement stores. It is not reactive with dope and does not shrink. Depending on the color of the finish and size of the ding it will be almost invisible. The best way to avoid having to fill or fix any dents or dings is to not make them in the first place! Keep your workbench clean and clear of tools and other items that can ding a model and you will not have to worry about fixing them later …
I will try to put the following info in a very general building order and try also to explain the reasons behind what I use and how to use it. Start with a perfect bare bones airplane. Yeah, right. Spend extra time sanding and candling the surface of the airframe until it is as close to perfect as you can make it. Candling is a process in which you hold the airframe up to an incandescent bulb and bounce light off of every area, working very slowly and being extremely critical of any shadows, low areas, high areas, etc. When you identify an area that is not perfectly smooth, stop and detail sand that area to blend with the surrounding areas. This process can take hours, but the result is a much more perfect airframe on which to apply a finish.
I cover all my wings, flaps, stabs, elevators, and some cowls with polyester tissue. I prefer Polyspan brand but I have been having trouble finding a source for it lately. Bob Hunt informed me that a modeler named Larry Davidson carries Polyspan and also a new version of the material called Polyspan Lite. I have used a lot of the polyester tissue that is available from Tom Morris with good results. This same material is also available from Jim Snelson at Control Line Central.
Why polyester tissue? It is light, tough, seals and fills fast, and will form around compound curves readily with the aid of a MonoKote iron. It allows you to have fewer seams and less piecing. (Remember, everything shows with a transparent finish!) An entire article could be written about covering with polyester tissue—but not this article.
Silkspan or silk should also work; I just don’t care to use them, although I do use Japanese Tissue and lightweight silkspan for covering fuselages.
Okay commercial time. Bob Hunt’s Stunt Flyer Video Magazine Volume 1, Number 3 has a segment featuring Mike Spedaliere, who is a true master builder. Mike explains and shows three great building methods you should be aware of. The first is a method that Mike uses to cover with silkspan or Japanese Tissue that yields a virtually seam free appearance. The second is a method for installing balsa fillets, and the third is the gluing method I mentioned earlier. This is a very professionally done video. I am sure you would enjoy it.
Here is a close up of Jamison canopy and wing fillets.
Polyester tissue neatly and seamlessly conforms to compound curves.
Okay the masterpiece is covered. The next step is applying the fillets. I prefer to apply the fillets after everything is covered and a couple coats of dope have been applied to the airframe. What I want to do is briefly describe my method of applying fillets and how they relate to transparent finishes.
I use three products, two of which are readily available. The first is Top Flite White Micro Balloons, the second is Bob Smith Industries 20-minute Finish Cure Epoxy and the third is Dave Brown Products’ Phenolic Micro Balloons, which are brown in color. If you cannot find the Dave Brown product, I have been told that West Systems carries some, but it is only available from them in larger quantities.
A bit about the 20-minute Finish Cure epoxy: It is very thin and soaks up a lot of micro balloons and is very easy to sand. FYI, Bob Smith products are the ones found on the shelf with the local hobby shop name on the package.
I am going to take a second here and explain why I use this method. When blending the brown and white micro balloons I can adjust the color to match the surrounding wood. This material is very light, and quite durable; I have had no cracks in several hundred flights on four models.
Be sure to mask the areas in which you will apply fillets. I mask over the wing chordwise, and lay the tape out on the wing just far enough from the fuselage to allow the radius of the fillet to be formed. The next piece of tape goes on the fuselage and follows the curve of the wing, just far enough above the wing to allow the fillet radius to be formed.
Mix only enough material to fillet two wing panels, then mix more material and apply the fillets to the other two panels. I fillet all four stab panels and the fin at the same time with one mix. In other words I don’t mix too much at a time.
How much material should you mix? A lot will depend on how large a wing you are doing and how large you want the fillet. On full size Stunt ship I will usually mix 25 to 30 drops each of epoxy and hardener in a plastic mixing cup and I use a 6-inch piece of 3/32 inch diameter music wire with the ends rounded as a mixing stick. This tool is also handy with which to apply the material to the model.
I keep a squeeze bottle of premixed white and brown micro balloons tinted to a light tan (medium balsa) color. After mixing the epoxy completely, I slowly add the mixture of micro balloons to the epoxy; I want a fairly thick consistency at this point.
Fin and stab fillets and the cloth hinges on the Jamison are almost invisible.
I then add either white or brown balloons to get as close to the required color as I can. Adding balloons also thickens the consistency of the mix. I want a consistency that allows the material to hold a “peak” as I remove the mixing tool.
Be aware that the cure time is lengthened greatly with the addition of the micro balloons. Spread the mixture onto your fillet area. It does not need to be even at this time; just try to get some material all along the area.
Now take out your specialized fillet forming tools … Huh? Okay, a ball bearing glued to a piece of scrap wood, a round flashlight bulb, or nicely rounded piece of scrap wood will do the job. If you use any of the above use it wet. Water or rubbing alcohol will work fine for this; just keep the tool clean and wet.
Now remember your application will be staggered time wise and at about 45 minutes after installing the fillets, remove the tape and feather the edges and ends of the fillets with a wet finger. Do this gently and try not to let your finger get into the actual radius of the fillet. You are looking to just smooth the edges where the masking tape has left a “lip.” When you have finished, let it all set up for 24 hours.
The way I gauge if the material is set is to roll the left over mix in my palms to form a ball and check the hardness periodically with a fingernail. It usually takes 24 hours before you cannot dent it.
By the way, this mixture works great to fair in canopies as well. When you are sure the fillets have cured thoroughly, sand them well using sandpaper wrapped around a dowel that is the same radius as the fillet. Epoxy can be a challenge to sand, but the micro balloons help make this process a bit easier. After the finish is applied it will be difficult to distinguish the surrounding wood from the fillet. Remember, everything shows.
Again the products I will talk about are ones I use and prefer. I use Randolph un-tinted non-tautening nitrate and butyrate dopes. I am sure Brodak, Sig, Certified, or Superior will work fine also. I use nitrate dope on the bare wood as a sealer and adhesive to attach the covering. I find it easier to use for this and it is much more “sticky.” I also apply two thin coats of nitrate dope over all of the covering—especially the polyester tissue—and two coats over the sanded fillets. It sticks well to the Polyspan and fillets and gives the butyrate something to grab to.
I am not going to give a step-by-step procedure on building up a flat surface finish; you all have your favorite methods. Just remember, use no gray or silver here; it has to be clear. I use the good old dope and sand method even on colored (not dyed) finishes. The first dope with pigment I use is the base color coat. Again if you feel the need for a filler use zinc stearate as it is undetectable under the finish. Just remember to apply a light coat of clear over the last filler coat.
As you near the end of the build-up coats, candle it often looking for shadows (low spots) and the little sparkles also reveal low spots. Sunlight works best for this but you can use 100 watt incandescent bulbs in a reflective holder; fluorescent does not work well at any wattage.
When you are satisfied vacuum the airframe or use low pressure air to blow off the dust. Then use a tack rag, and then wash it. Huh? Well sort of. There are automotive products available that do work, but I picked up the following tip from Phil Granderson: use Windex to clean the airframe. Wash and dry the model at least twice, tack it again and you are ready for the fun part: transparent colors.
Now I am going to ramble a bit. Those of you who know me, or know who I am, probably also know I like yellow; loud, bright, yellow. I have used other colors but always came back to yellow. Before I was really into modeling a good and dear friend of mine, Gordan Delaney built an ST .46-powered Stunter, and it was yellow. Not transparent yellow, just lemon yellow with red and blue trim. I thought it was the most beautiful stand out in a crowd model I had ever seen. Then, of course there was his magnificent yellow twin. Okay with that out of the way on to the finish.
The author uses and recommends Aliphatic Resin glue, such as Sig-Bond or Titebond, on all external wood seams.
Pete uses Bob Smith Industries’ 20 Minute Finish-Cure epoxy and various color micro balloons to make the fillet material.
Here are the canopy and wing fillets on Pete’s Rondinelli Venus.
I chose the transparent look because of the weight, or lack thereof. There is no pigment in the base color, and the beauty, no matter what color is used is amazing. I love the look, wood grain, sun through the open bays, and the amazing number of colors that are available.
I have used two “dye” products. One of these I’ve tried in a very limited manner, so I will write about the other one … If you know of similar products please share your knowledge with me and the other PAMPA members.
The products I use the most are from House Of Kolor and are named Kandy Koncentrate. They are automotive paint products and have UV blockers; they do not fade. They are available from most auto paint stores. If you can’t find them locally, check the House Of Kolor website for dealers close to you. The Kandy Koncentrates have a part number starting with K-K followed by two digits for the colors and they come in handy 8 ounce round cans with round screw top lids. They are easy to open and easy to pour.
One can of Kandy Koncentrate is enough for three or four classic size models at least. It is very concentrated and does contain a small amount of transparent pigment. Do not strain this out!
Ask the dealer to allow you to look at the House Of Kolor color chip catalog. The colors are shown over various base colors and unfortunately they are not shown over white. You will have to look closely to decide which color you want to use. The bright yellow I use is called Lime Gold, and it appears as gold if sprayed over silver. This product mixes perfectly with all the normal dope including nitrate and Aero Gloss.
The method: I admit I am not very good with mixing ratios and amounts, so this is going to be an “about that much” sort of thing. Start with about 1 1/2 ounces of the dye. Mix it with about 8 to 9 ounces of reducer and about 4 to 5 ounces of dope. Thin it and retard it for your particular equipment and local weather conditions.
You will want to apply the colored dope in two fairly light coats. This is just to dye the existing layer of dope. It goes on evenly without strips or splotches and does not darken much with additional coats. Okay, since you just put a lot of reducer on, you should let it gas off for a day or two. Then follow with a light coat of clear dope.
You are now ready to mask for trim colors. By the way I use dope from the bare wood up to and including the top coats; I am sure automotive clear coat on top will work just as well. I use some Sig colors that are no longer available, as well as Randolph colors and auto toners mixed in clear dope. For you guys who like to use dope I have the good fortune to live very close to a company named Spencer Aircraft; they are a full line Randolph dealer and have at least two very knowledgeable Randolph factory-trained employees.
I’m going to throw out some more really neat products. Dry pearl powders come in many colors, they are nearly weightless, and they are sold by the gram. Again House Of Kolor has this product available. They can be mixed in the dye coats, under the dye, over the dye or in the top coats. Use your imagination. Randy Powell has used these more than anyone else I know. Some of his combinations are really “cool” (Randy word).
There are also three sizes of metal flake that are also available in many colors. The key word here is: Experiment!
Pete’s Venus is covered with polyester tissue applied with Randolph dope and Kandy Koncentrate Lime Gold.
Again use your favorite method, or do what I did and ask an expert! Phil Granderson explained how he rubs out a model and let me take notes (slow), but then he published his great method of rubbing out a model in his “CL Aerobatics” column in Model Aviation magazine in March of 2007. I use the tools and products he recommends and uses. It is fast, easy, and simple. You can rub out a full-size Stunt model and wax it in but four or five hours of work and it will look shiny and “wet” when you are finished.
Here are the Kandy Koncentrate KK-11 Apple Red and KK-02 Lime Gold products. The Lime Gold is the bright yellow that Pete uses on most of his models.
This article first appeared in the January/February 2009 issue of Stunt News and has been preserved as part of the PAMPA digital archive project.
