I'm using balsa wood for a long highway bridge on our HO layout. Not for the road bed or piers but for the railing and the 'carriers' or concrete beams below The bridge has several curves and elevations and the balsa is easy to soak and shape. . Balsa is easy to work with but not very strong. I wonder if a coat of varnish would soak in to the porous wood and strengthen it Or perhaps some other kind of paint
Ben and grandson Mitchell