JP,

another thing to to consider is that traditionally the skins used to be glued up from 2" to 4" balsa sheets. Once the sheets were bonded to form the skin, it was sanded smooth on both sides, vacuumed and tack clothed prior to adding glue to the side bonded to the core. This method works but can have the disadvantage of producing hard edges at the sheet splice joints.

Nowadays, some of us, have gone to an approach which carefully splices the sheets together but they are held together with painters tape rather than glue. The skin is flipped and the same prep is given to it after which it is bonded to the core. If one uses laminating epoxy rather than expanding polyurethane, the glue just seeps in enough into the joints to keep everything together once the painters tape is removed. This works especially well with thin skins such as 1/32". The use of foaming polys might also be possible but I haven't tried it. The risk is that it may seep out of the joints leaving a hard line of glue that doesn't sand well. The use of epoxy leaves a virtually seamless uniform balsa outside surface which sands and finishes quite nicely. That said, expanding polyurethane glue has its virtues and advantages but I feel it might require the skins to have pre-sealed joints along the splice lines.

A few more things to think about... ;-)

David