by D-Mac »
Sat May 22, 2010 9:42 am
It is salt that is being leeched from the bricks and as it comes to the surface, it becomes visible as a white staining. This effect is called "efflorescence" and if you do a google search, you will find plenty of information on it, including how to remove it (the top page on the google search was from this forum incidentally, so you could try here first).
Dylan.