In built-up r/c sailplane wings, which have to take winch loads of hundreds of pounds on launch, the standard practice is to use vertical grain balsa shear webs the width of the spar on the inner part of the wing (where bending stress is highest) and to thin the shear webs from full-width to 1/16" from the inner part to the wingtips to save weight. On the inner part, the spar/shear web is also wrapped in Kevlar thread to keep the spar/shear web from "bursting". Epoxy thickened with microballoons is used to assemble the shear web/spars.

You judge a strong launch by observing how much the wings flex on launch and also how much wrinkle you get in the covering.