Try using urethane glue. It is marketed under various names. I used to get it at Home Depot when it was Pro-Bond. Now it is called Ultimate glue(same thing new marketing).

Urethane glue will expand when it is curing. This makes for great bonding as it will leach into any crevis or pocket of foam. It will penetrate the foam about an 1/8".

I make my sheets and just use masking tape to hold the sheets together. Use good quality 6lb balsa. I do not glue the edges together. This save time more then anything. The expamding glue will seal the edges. Seal the balsa with the cheapest hair spray you can find on the gluing surface. After they dry lightly sand with 320 or 400 paper and vacum and tack rag them clean. Then sand your cores to get the flash and iregularities out and then vacum them clean. Use 1" wide strips of light carbon fiber or c.f. tow for spars, 2 top and two bottom about 20-22" long and a small square of c.f at the aileron cutouts top and bottom beween the spars. Run a light bead on the foam where the spars go and set the c.f. spars and c.f. for the servo cutouts in place. It takes about 1 ounce of glue per panel. Use just enough glue to make a sheen on the surface of the wood. Use an old credit card to spread the glue. If it looks like it soaked in the wood add a little more it wont take much.

Here is the secret to making this stuff work good. Lightly mist the cores with a water atomizer. The moisture is what makes the glue kick or set and expand. Set you cores as you normally would and weight them down. Let them cure for at least 15-20hrs.
DO NOT use urethane to glue L.E. or tips. the glue will make the edging seperate from the edges, use white glue here.

My last set of wings 950 sq. in came out at 14.5oz finished ready to fly with MK and 9411 servo's. And this was with out no coring or lightening of the cores. Retracts will be heavier. Much easier then using and mixing epoxy and the expanding qualities make ideal for this purpose.

Smooth FLying...

Wayne Galligan