Covering a foam wing with brown packaging paper 

This was a repair job. The original wing was an experiment. It had no spar. I inserted a spar in the center section and this was recovering this section. I discovered that polystyrene covered with brown paper will fail in compression. A spar is needed to prevent this issue.

It appears he doesn't reply to comments, or RU-vid is having issues again and he never saw your comment. I am sure the reason he primes the paper with water is so less glue is needed, which is likely thinned a bit also. As to paint, most use acrylic paints, but the paper and glue combo does make it possible to use almost any paint that won't add significant weight. That is assuming the paper skin is preventing the paint from soak through to the foam. There are more than a few other videos like this that go into more details.

@@wattwaster5936 Hi, I am sorry for the late reply. Priorities have shifted due to health issues (pernicious anemia) and a 20% reduction in income (economic byproduct of c-virus). I found by experiment that pre-soaking the brown paper (5 min) allowed it to fully expand. I hang the paper up until it stops dripping then apply the glue. The white glue seems to penetrate better and results in improved adhesion. You should also notice the paper wraps the wing completely with a generous overlap on the leading edge. Thin the glue until it is easily paint-able. While the glue and paper is still wet, I wipe the completed covering down with a moist cloth. This gets the last of the bubbles out and removes any white glue from the exterior surface. Within a short period (30 min) I coat the whole surface with a water based urethane (which dries at the same time as the glue to form a hard skin). The trick is to allow everything to dry slowly (in the shade). In warm weather do this in the evening and allow overnight to dry. Once dry, fill any hollows with lightweight spackle, sand smooth and paint. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4wDGqfhrEEw.html start at 4.30. Also ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-C9jWIAJLxgw.html start at 3.00 and ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hpz5sO37Nzo.html

@@flyingweed9671 Nice details the other videos in my playlist often don't get into. Thanks and I know what you mean about life and priorities. I am an old guy and feel your pain. I have plenty of my own to deal with.

@@flyingweed9671 очень не качественная работа

Yep. It's heavy when wet, but it drys and becomes light and strong. The trick is to dry slowly and evenly to prevent warping. When the wing fails, it fails on the upper surface, in compression.