If you use it straight you will end up with lumps of the stuff in places after you brush it on. When you cover it will turn into a gum under the covering and remain visible. Thin the stuff. It works a lot better if it's slightly more viscous than water. Another substance that does a good job at sticking covering is clear dope. It's almost impossible to get Balsa Rite in California due to an idiotic materials substance law the voters stupidly enacted a few years back. Good auto paints are also hard to get in most of the state.