The suggestion is the salts expand somewhat upon drying. That is one of the reasons that road salt will deteriorate the surface of concrete pavements without air entrainment.
There are other factors that bring in water other than by gravity via rain. Salts have affinity for water and the cement in the blocks may contain some. The white stuff shown is some form of salt(s). That affinity will "draw" moisture from the soil below by differences in vapor pressure's (caused by temperature differences, etc.) well as by capillary attraction. Moisture in the air also has been known to end up "wetting" salty areas. Such an example is the wet floor slab in my garage in spring where salty water earlier has dripped from the car in winter. That moisture came from the air probably, but see below.
This effect probably is similar to plastic floor covering systems (as in gymnasiums) which sometimes come loose with the mastic taking on moisture, sometimes blamed on that salt concentration remaining in the top of the slabs by drying some before the floor covering is placed. I've measured that and it is high in concentration at the top as compared to bottom of slab. Osmotic pressure differences come into play also. Yes, concrete makes a good osmotic "membrane". You remember that high school chemistry demo with the egg shell membrane? The pores in concrete work the same. These pressure differences can be quite high.
I won't say I have all the answers, but I have seen some real problems generally in this field. For instance explain how the bubbles in that gym flooring mastic contain water under pressure. If you measure that pressure, it is many inches of head above the floor. Certainly never got there by a water pipe breaking somewhere.
The efflorescence and deterioration of this post subject probably is related to those other problem factors with concrete mentioned.
Here is just one of the references one might look at on this subject.
cvg, when was the wall built? I toured a CMU plant yesterday and they said that during the building boom a few years ago, they were sending out 2-day old blocks for immediate construction. Could be that the blocks were too young and got banged up a bit.
I see lots of deteriorated CMU, and I'm used to seeing really crumbly faces - like being able to easily pop big chunks off with my awl. Can you do that here? Even sound CMU can be poked at occasionally.
