Efflorescence

Common card · No. 273003

In chemistry, efflorescence (from the Latin efflorescere, 'to flower') is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an internally held salt in water or occasionally, in another solvent. The water, with the salt now held in solution, migrates to the surface, then evaporates, leaving a coating of the salt. In primary efflorescence, the water is the invader and the salt was already present internally; secondary efflorescence is the reverse process, where the salt is originally present externally and is then carried inside in solution. Efflorescence can occur in natural and built environments. On porous construction materials it may present a cosmetic outer problem only (primary efflorescence causing staining), but can sometimes indicate internal structural weakness (migration/degradation of component materials). Efflorescence may clog the pores of porous materials, resulting in the destruction of...

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