Friend of a friend closed up his shed door and put in 2 windows instead. New blockwork has to be matched in to existing which was plastered a few years ago by another. On hosing down the wall today all these crack like features appeared as the water dispersed. A plasterers nightmare I suppose. I see this alot in external plastering anywhere I go driving along the road looking at new houses. In dry weather they look good but when wet its totally different. From ye're experience and knowledge what could have caused this to happen in the pictures attached.