Usually, it is best to simply brush the salt deposits off the surface with a stiff broom. The use of water is not always recommended. The water can dissolve some of the salts and actually drive them back into the masonry. They will subsequently re-appear when this secondary water evaporates. In the most severe cases, dilute solutions of muriatic acid can be used. However, BEWARE of this method. Muriatic acid can cause serious eye and skin burns. The vapors are also very toxic. Muriatic acid, improperly applied to a masonry surface, can 'burn' the brick and cause discoloration.
Brick that is still experiencing efflorescence should not be sealed. If you do this, there is a possibility that you can actually damage the surface of the brick.
The sealer can actually block the movement of salts to the surface of the brick. Now, you may think that is not such a bad idea. Well, here is what can happen.
The salts work their way to the sealer at the surface of the brick and stop. The concentration of the salts increases as the water evaporates. In certain instances, the salts begin to crystallize. This process of crystallization can create enormous pressure on a microscopic level that can actually cause the face of the brick to pop off or spall.
Over the years, I've seen many different spellings of efflorescence. Here's my growing list: effervesce, effervescence, effervescent, effleresants, effloreflance, efflorescence, efflorressance, effluorescence, eflorescence, eflorescents, ellforesce and ifflorescence.