Unfortunatlety efferfesence is caused by water bringing the natural salts in the material, either from the clay or from the manufacturing prosess to the surface. Washing off with water will get it off, but as you wetted the area an awfull lot it will most probably come out again in the future. If you look very closely you can see it's almost like small worms as the salts come out from within the brick/blocks via the small pores in the surface