Efflorescence - causes

Efflorescence is a white crystalline deposit that forms on or near the surface of concrete, masonry, grout and other cement-based materials. It is the most common post installation condition in tile, stone and brick masonry installations. Efflorescence can range from a cosmetic annoyance that is easily removed, to a serious problem that could cause adhesive bond failure or require extensive corrective construction and aggressive removal procedures.

Causes of efflorescence 

a. Presence of Soluble Salts

b. Presence of Water (for Extended Period) 

c. Transporting Force (Gravity, Capillary Action, Hydrostatic Pressure, Evaporation, etc…)

Sources of efflorescence:

Also from:

> Hydration of Cementitious Materials (Calcium Hydroxide)

> Calcium Chloride Contamination Sea Salt (Airborne, Sand)

> Mixing Water (Calcium Sulfate or Calcium Chloride Water Softeners)

> Cement Accelerator or Anti-Freeze Admixtures (Calcium Chloride)

> Acid Etching and Cleaning Residue (Chlorides)

For further more details, refer to: https://annayyachandrashekar.blogspot.com/2018/07/efflorescence-testing-method.html

Many thanks to Google.com and Doc88.com.... from where the details are referred.