Willib,
In my younger years I used to build model aircraft. The wings were made out of styrofoam, covered by balsawood. This sandwich structure was VERY strong! A 2cm thick wing (strengthened in the middle, where the two wing-sections joined, with a bit of glassfiber and epoxy) could easily carry my weight (say, 50-60kg at the time). Impressive eh?
Don't see myself making a prop in the same way we used to make wings, but will surely follow your experiments with interest.
Peter.