I have "pockets" on my exterior concrete block walls that I have previously hollowed out. Those could be voids left my old electrical boxes or drain pipes that I have since relocated...or new voids opened up in order to tie a new fixture into existing vent stacks.
I hired a concrete contractor to repair these walls.
Large voids he filled in with concrete mix, solid fill.
Smaller voids like electrical boxes and such, he stuff newspaper into adjacent hollow blocks to avoid spilling over, then fill with stucco mortar mix. Specifically the "SAKRETE 60 lb. Mortar Mix Type S".
My question is, when I am attaching wood furring strips to the concrete walls, is it OK to drill holes into the patched areas filled with stucco mortar mix and drive Tapcon screws into them? Or should I avoid those patches and only drill where I have original blocks?