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).
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!