Alan,
tks for your reply, and yes i would have thought this could have been a problem on new er bricks , however the buildings in question are prorbley around , at a guess 25 yrs old, I will try and take a pic when I am next passing.
Another point that may be effecting them is that the affected bricks all tend to be where overflow pipes come from the wall and at some point have had water running down them.
Geoff