I would think that anything loose will need to come off; the mortar won't stick for long to a failing substrate.
Preparing concrete block for stone veneer
As I started to strip paint with my pressure washer the other day. I noticed that under the paint, I seem to have two skim coat layers on the block; at least the white stuff in the picture feels abrasive like mortar and it crumbles like a masonry product. Is stripping the paint alone sufficient to achieve an acceptable bond? Should I try to strip away the white stuff before I apply the cultured stone veneer? Should I try to strip away both layers of mortar to expose the concrete block?
