climbing epoxy cement climbing holds bouldering

Don't.drill them. That is why they have the little holes in them.

You should seriously consider other options. l doubt that the holds will stay on, & when they come off they will probably utterly destroy the surface. Plus u will never be able to rearrange them. It does not take much effort to construct a basic free-standing bouldering wall out of plywood. At the very least u should investigate drilling bolt holes instead, or floating a sheet of plywood in front of the wall to drill into. Though possible, l would not recommend drilling directly into the concrete.. u will need special bolts that u will also have to somehow fit to the holds, & even then l have my doubts about how well they'd hold.

If u r absolutely set on gluing them on. Gorilla Glue maybe?

if you must glue them do it with JB weld