Does anyone know whether 3/8" balsa core material (sandwiched between
fiberglass skins) can go over a 35" span on a deck without any
structural bracing?

One area of the deck has some water damage and is "kind of"
delaminated. The problem may be coming from an improperly sealed
inspection hole. I am trying to drill many holes on the deck and
inject thickened epoxy into the core to fix the damage. But I discover
that the balsa core is only 3/8" thick (the thickness of the deck with
core and skins is only 1/2"), and it needs to go over a 35" span in one
direction without any structural bracing (the span over the other
direction is around 9 feet without any structural bracing).

Before I spend time injecting epoxy and all this, I need to figure out
if 3/8" balsa core is strong enough to go over a 35" span. If this is
not strong enough, I will have to abandon this project and leave bad
enough alone (I don't have access to the bottom of the deck to add
structural bracing); the reason is that the problem will come back even
if I fix it with injection of epoxy.

Any idea? Thanks in advance for any info.

Jay Chan