Next, the ribs and nose strip are coated, in the front area, with casein glue across their entire length (Position 1). To this effect, use commercially available casein glue, such as ´Ponal´ or a similar brand. Apply the casein glue generously.
Now, place the covering (Position 2) vertically onto the nose strip, as shown in the illustration. Then, the covering is pressed onto the nose strip with the hot smoothing iron (turned to maximum heat). After a few seconds, the fluid in the casein glue will evaporate and it will start binding. You can see this, as the glue runs out of the gaps, creating bubbles. Now, remove the smoothing iron and use a soft cloth rag to press the wood together (Caution - hot!) ). After a short time, as soon as the glue has cooled down, the parts will have bonded onto each other. Continue working from rib field to rib field. You have enough time. Even if the casein glue has already cured, it will soften up when heated. Then, allow all parts sufficient time for cooling down.
After the covering has been glued onto the nose strip in this way. You can now slightly moisten the outside of the covering with a wet rag. By this, one side of the covering will stretch and start arching over the wing.
Do, however, take care not to apply too much moisture so that the covering will not undulate (Position 3). Then, you can generously coat all ribs and spars with casein glue (Position 4).
Subsequently, starting from the nose strip, the covering is again heated with the smoothing iron and fixed with the cloth rag as long as the casein glue needs to cool down. Then, consecutively work down all rib fields until the covering has been completely bonded in place.
Should the balsa wood of the covering discolor from being scorched, you can later grind down these spots. Let the wing cool down and cure completely, at best over night. In this way, subsequent wing torsion is prevented.
A wing “treated” in this way has the advantage of being completely tension-free, since the covering has been appropriately “shrunk on” by the heat and moisture, adapting itself to the surface contours.
The wooden surface is also slightly hardened and, thus, less sensitive and, additionally, the required grinding is minimized.