Bonding to a glossy, fully-cured epoxy surface (the left side of the photo) will result in a weak joint. The usual method of surface preparation is to abrade the surface thoroughly using sandpaper prior to any bonding step.
Sanding works, but often requires cutting into the topmost fabric ply to really remove all the gloss. It is also dusty and slow, and it can be difficult to fully sand the surface down inside pits and opened blisters.
But there is another way.
Do you have access to a bead blast cabinet? The quick approach is to gently blast the surface. The glass beads evenly abrade every bit of the surface, including pits and voids (the right side of the photo), leaving it ready for bonding. Just blow off the dust and proceed with subsequent lamination or surface fill.
The glossy surface on the left is untouched, and will provide a poor bond. The right side has been bead blasted and will give a good grip.
Dan Horton says he is “just a homebuilder”. He has been a pilot more than 30 years and currently flies a custom RV-8.