Numerous air gaps existed in the last layup due to the radius required on the outboard edges of the stiffners. In hindsight, I should have rounded the edges of the foam before the layup and that would have helped to some extent.
I drilled entry and exit holes in the air gaps for epoxy injection where required on both horizontal and both vertical stiffners.
The shop temperature was 80 deg F and the humidity was 45%. I mixed up a small cup of epoxy and filled the air gaps using a syringe to inject the epoxy.
