Hello room;

I was wondering if you can glass right over foam, without having to sheet with balsa.

Craig.

Yes you can. Combat Models F-16, F-18 are made out of foam.
Get some light spackle, spread over the foam so it fills the voids between the beads, sand back down to the foam so it's nice and smooth, then glass with an epoxy finishing resin. DO NOT use a polyester resin, it will melt the foam. If you have a big wing you might have to put some carbon fiber strips for strength. That is how the CBM F-16 is.

What ya going to build?

I am planning on building a 96in Lancaster bomber, with 4 .25's. The plans do not show balsa over the foan on the wing or on the foam fuselage parts. I may sheet it any way just for some added strength.

Craig.

Sounds like a cool project, but for a plane that size I think sheeting would be needed.

Good luck.