Such "new building bloom" on structures is typically easily removed during final cleaning prior to the application of masonry water repellents, and should no longer be an issue. If efflorescence reappears or persists, it is evidence of water entering the wall by some means, and not necessarily through the face of the masonry.
Site walls, however, are exposed at top and both sides, and do not typically receive a water repellent treatment. When exposed to damp weather, compounds within the cmu, mortar, grout, and concrete will likely dissolve and migrate to the surface as evaporation occurs. Water from irrigation can contribute by not only wetting the wall, but may also contain salts of its own, resulting in a persistent, heavy build-up of efflorescence.
Concrete or masonry materials contain a finite amount of soluble compounds. Left untreated, efflorescence from these materials will diminish and end. In and of themselves, the efflorescence is usually light enough to be washed off by rain over time, with subsequent wet/dry periods leaving diminishing amounts of efflorescence. You'll notice the great majority of site walls, while exhibiting normal weathering, remain attractive, durable fences.
An installation with persistent efflorescence is indicative of either a continuing intrusion of water, as already mentioned, or a continued supply of soluble compounds. Irrigation has been noted as a source. However, the very soil upon which the masonry wall is built may also be the source. "Through capillary action, salts present in the soil may rise several feet above the ground, producing an accumulation of salts in the masonry."1
For the rare instances of stubborn deposits, commercially available efflorescence removers can be utilized. Optional additions of integral water repellents can mitigate but not entirely prevent all instances of efflorescence.
Efflorescence from the constituents of concrete and masonry is the result of naturally occurring salts and typical exposure to moisture, its remediation is a common, successful process of cleaning and control for buildings, or simply a matter of time for site walls. Sources of the efflorescence are not limited to the masonry wall materials, but may also, or instead, originate from other sources: potable water, soil, or adjacent structures.
1Control and Removal of Efflorescence, TEK 8-3A, National Concrete Masonry Association, 2003
Angelus Block Co., Inc. supplies this information as an educational aid in understanding the benefits of concrete masonry construction and our products. It is the responsibility of the user to obtain engineering or other advisory services from licensed professionals as the basis for incorporating into any project any information, detail, or product offered herein.