Efflorescense is not specific to concrete. Though, often times concrete products are more likely to effloresce than clay products. The first post indicated that the bricks were made of concrete. When quality brick pavers are made, the manufacturer usually uses some sort of efflorescense control in the concrete mixture. This only aids in stopping efflorescence, and doesn't guarantee against it.
When grouting is involved, which is the case here, then one must consider the possiblity that the grout wash has left a thin film of mortar overtop of the bricks, moreso around the edges. If that is the case, then i'm afraid that only time and mother nature will heal the pavers. My experience with sloppy grout is limited, and i've only had one instance where concrete was carelessly spilled on a brick driveway of mine. Concrete sticks to rough concrete(pavers) pretty well, anytime we've been asked to remove it, it's come at a cost to the homeowner. Not just in our fees, but in the overall look of the effected areas. My advice when dealing with this situation is either preventative maintenance(hiring a specialist in the first place) or letting nature take it's course and allowing the spill=over to natural wear off.
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