This is something that really irks me. How do you explain to a customer that has just spent xx thousands on a retaining wall, that the color they picked, purchased and paid to have installed will now be dappled with white powdery looking crap for the next three years - or maybe forever. I know what it is...I have heard the explanations from block suppliers all over town. But, some (batches) of blocks have it, some don't. I believe manufacturers should set aside stained blocks or at least classify them as grade B's or something. Bottom line, blocks with efflorescence are embarrassing to a meticulous, high dollar installer as myself. It really s*cks! Had to vent....anybody else concered about it or do you just say oh well!