Where does efflorescence collide?

In building science, efflorescence is the whitish crystalline salt deposit that appears on the face of brick, stone, or concrete masonry when water moving through the porous material carries dissolved salts to the surface and then evaporates, leaving the salts crystallised behind. Brocken and Nijland's 2004 study of white efflorescence on brick and concrete masonry separates the primary bloom that forms during a wall's first drying from the sulfate deposits that recur later. The referent is a durability and appearance defect in which evaporating water DEPOSITS salt onto a surface, which is the opposite of the chemist's meaning in which a crystal gives up its own water, the two joined only by the shared image of a powdery bloom.[1]

Unit

The amount and extent of salt crystallised on a masonry face

Recovery means

Deposits can be brushed or washed off, but recurrence depends on the salt source and continued moisture, so removal is not a permanent cure

Measured by

Rated by visual coverage of the face and by chemical analysis of the salts (e.g. ion chromatography) and the moisture and salt load in the wall

In chemistry, efflorescence is the spontaneous loss of water of crystallisation from a hydrated crystalline salt exposed to air whose water-vapour pressure is below that of the hydrate, so the crystal sheds water and crumbles to a powder, the exact opposite of deliquescence. Standard examples are washing soda (sodium carbonate decahydrate) and Glauber's salt, which lose their lattice water and dull to a crust in dry air, as set out in the Van Nostrand's Encyclopedia of Chemistry entry. Here the construct is defined by water LEAVING the crystal, the reverse of the masonry meaning where evaporating water leaves salt on a surface, making the shared word a trap.[2]

Unit

The quantity of hydrate water a crystal loses to the surrounding air

Recovery means

Not applicable

Measured by

Followed by mass loss and thermogravimetric analysis, and predicted from the gap between the hydrate's dissociation vapour pressure and the ambient humidity