Some sort of a moisture problem behind the wall. Don't know if it is from a leak in the roof, or rising damp. but basically what has happened is that moisture was behind the concrete rendering, and then after several cold winters, when the temperature falls below zero, the moisture freezes and cracks the concrete and make the bricks brittle. Force of nature, incredible So I have a little job added to my list of things to do , or Project #728 :-)