Spalling and Efflorescence
Efflorescence is the product of dissolving internal salt by water or sufficient moisture and migration of the salty water to the surface of the wall. Depends on the weather and humidity, the water will evaporate and leave the salt behind that forms the efflorescence.
When it occurs, it indicates there is water/moisture that should be corrected to prevent the cyclic occurrence, which is harmful to the material/structure that contains the salt.
To correct/eliminate this problem, the first thing is to identify the source of water or cause of high humidity/moisture and cut off the capillary path. The linked article at the end addresses these issues and suggests ways to prevent the problem from recurring.
Per the article, some of the ways to remove efflorescence include:

Pressurized Water: Applying pressurized water may dissolve efflorescence quickly. If you use water, dry off the water from the building material after application. If you fail to remove the water, crystals may remain that can cause efflorescence to reappear.


Diluted Vinegar: If you’re in a pinch, using household diluted white vinegar can be used on efflorescence. It’s less harmful than industrial chemicals and you most likely already have vinegar in your kitchen.

Brushing: With a strong brush, you can remove efflorescence with ease.&quot;


Note that compared to method 1, methods 2 and 3 are patchworks, but they could work if the capillary path can be blocked effectively.
Please read this article for more information.  https://www.nitterhousemasonry.com/tips-advice/what-is-efflorescence/