We've got you covered! A complete guide to the perfect finish

Model Airplane News, Nov 2002 by Yarrish, Gerry

Once you decide to build all-wood airplanes, you need to apply a finish over the built-up airframe. You can choose from a large array of materials. The two main types are Iron-on plastic films and fabric-covering material. Plastic film covering comes with heat-activated glue applied to its underside, while fabric-covering mater-- lal Is available with or without the glue applied. Fabric covering is also available with and wihout color applied to Its outer surface.

This guide covers the various materials and the basic techniques used to cover a model. Whether you want a scale, paint-- over-fabric finish or a shiny, iron-on plastic film covering, the first step is always to prepare the basic wooden structure. No finishing technique will cover up poor building practices.

PREPARATION

To obtain a smooth finish, you need a smooth base. It is always better to have an average-looking finish applied over a superior base structure than it is to have a superior finish over a badly prepared base. Are there any rough spots on your model? Close your eyes and feel its surface with your fingertips. How about raised seams between balsa sheets? Dents and dings must be filled and sanded smooth. The biggest difference between good-looking models and great ones is sandpaper. Start by sanding the entire model with 150-grit sandpaper, and use a tack cloth to wipe away the dust. Sand any raised edges until they are flush, and remove obvious rough spots. Use model filler to fill voids, seams and dents. To help the filler material bond to the wood, moisten the surface lightly with warm water. After the filler has dried, sand with 150-grit sandpaper, and use that tack cloth. Now repeat the process with 220grit followed by 320-grit sandpaper. Apply additional filler if necessary, and wipe the model once more with your tack cloth. (You can't wipe a model with a tack cloth too often!)

At this point, you can start covering the model, or you can apply a coat of Balsarite wood prep from Coverite. Balsarite seals the balsa surface and reduces the number of wrinkles that form after the model has been covered. Allow the sealer to soak into the wood, and let it dry completely before you sand it with 320-grit sandpaper.

APPLICATION

Covering material typically comes in 6-foot-long rolls, but some are available in longer lengths; this is helpful for big- and giant-scale models. For the average .40-size model, you'll need about 114 6-foot rolls. Always read the instructions, regardless of the type or brand of covering you use, be it Nelson Lite Film, Top Flite MonoKote, Hangar 9 UltraCote, Coverite's 21st Century fabric, Balsa USA's Solartex, or Sig Mfg. Koverall.

Though various covering materials may look the same, the temperatures at which they must be applied often differ. Some materials require a lower temperature for tacking and sealing and a higher temperature for shrinking.

Some covering materials come with a clear backing sheet that protects the heat-- activated glue and prevents it from sticking when it's rolled up. Don't remove the backing until you are ready to apply the material to your model. To use the material efficiently and minimize waste, cover all the large surfaces first; then, using the leftover material, cover all the smaller parts. The largest surface is the wing, so let's start there.

THE WINGS

It is easiest to deal with the dihedral of a wing by covering it in four pieces; two pieces for the bottom surfaces and two for the top ones. The seam left in the center of the wing can easily be covered with trim or simply left as is. Roll out enough material to cover the bottom of one wing panel, and leave 1-inch overhang all around. This makes it easy to hold and to pull the material when you tack it into place. Now set the covering iron to the recom-- mended temperature and let it heat up.

Wipe the wing down with a tack cloth and remove the protective backing from the covering material. Drape the material over the wing, and smooth it out. Using the covering iron, lightly tack the edges of the material into place, and gently pull out any wrinkles as you go. Use a crisscrossing pattern to tack each of the corners into place and to go around the edges. Each time you tack the material down, gently pull the wrinkles out and smooth the covering. If any of the tacked areas pop up, simply pull the material tight and reattach it with the iron. The edges should be completely sealed before you shrink the covering tight. Starting in the center of the panel, lightly run the iron over the covering until it tightens. Check for any remaining wrinkles, and apply heat to remove them. That's it! Now, do the same to the other bottom surface.

After the bottom surfaces have been covered, use the same technique to cover each wing's upper surface. The top is curved more than the bottom, and this makes it a little more difficult to remove all the wrinkles. Work slowly, and keep pulling the wrinkles out as you go. Once the wing is completely covered, run the iron over each of the ribs to bond the covering to the capstrips.