I’ve worked with epoxy quite a bit, and delaminating is one of its failure modes. That is, sometimes it flakes off cleanly without leaving much behind. Having

I’ve worked with epoxy quite a bit, and delaminating is one of its failure modes. That is, sometimes it flakes off cleanly without leaving much behind. Having said that, it’s hard to believe that there wouldn’t be traces of epoxy inside that very rough hole, or in the bare metal exposed by the drill bit. So it seems odd to me also.