These last, particularly vanadium, are said to produce green efflorescence on white or buff burned clay units, while other salts produce white or gray deposits. Efflorescence derived from complex vanadium compounds contained in the clay used in brick manufacture is not uncommon in the southwestern part of the United States. There are many sources for water-soluble salts with some salts more soluble than others. The movement of groundwater into building foundations and by capillary action, or wicking, upwards into masonry, stucco or concrete, is very often the cause of efflorescence. In the case where soil conditions exhibit water soluble sulfates, precautions should be taken to preclude the passage of this sulfate-bearing water to the structure.
Low absorption is the best assurance against efflorescence.
Properly graded aggregates, low water-cement ratio, good compaction and proper curing practices will produce concrete of maximum density and low water absorption. Sand and gravel, in their natural state, may or may not have been associated with salt bearing water or soil. If they have, and these salts are not removed by washing, this can be a possible source for efflorescence. Most rock, sand and gravel plants, however, are conscientious in washing material so that any contribution made to efflorescence from this source is negligible. The adherence, again, to a good concreting practice of low water-cement ratio, will help reduce the appearance of salts from this source.