Hello,
I'm setting up a Carrier for an Elfa shelf. I started drilling into a concrete wall with a newly purchased hammer drill, but at the last three markings out of 13, it turns out there is plasterboard on the surface, and something seems to be blocking on the backside, concrete? Above is a cube in the ceiling that we believe is part of the ventilation; I'm afraid to drill further. Will a universal plug and screw work in just those holes, or will it be too weak for the shelves? The other 10 screws are secure.
