A friend and I were discussing this yesterday. We passed a construction site (large building). Lots of steel beams were rusted, and they just sprayed foam over the beams. We decided that rust (coversion of Fe to FeOx needs transfer of oxygen. As long as the foam was gas impermiable, and the foam structure was sound, the rust process would not continue. However, if you paint over rust, the paint will not adhear. It will flake off and the rust will continue. I would not trust wax to be gas impermiable, and I would not expect it to stay on the bike over rust spots.