Efflorescence is a deposit of salts, usually white, formed on a surface, the substance having emerged in solution from within either concrete or masonry and subsequently precipitated by evaporation. It occurs most readily in porous concrete near the surface, and  often seen on floors and walls made of bricks and pavers. Efflorescence is not normally damaging, but it is aesthetically undesirable. Brocken and Nijland (2004) investigated the efflorescence process and its relevant parameters and reported that efflorescence on masonry is generally formed by (hydrated) Na, K, calcium sulfates or carbonates. Single and double salts commonly encountered are thenardite, Na2SO4, glaserite, K3Na (SO4)2 and syngenite, K2Ca (SO4)2 H2O.

 In mortar, sulfate generally originates from the calcium sulfate (gypsum, anhydrite, hemihydrate) added to control setting. Efflorescence of calcium carbonates, notably calcite, CaCO3 (formed by the reaction of Ca(OH)2 with CO2), often occurs on the surfaces of masonry or concrete elements. Efflorescence of gypsum occurs as a white foggy deposit on the surface of clay bricks. Efflorescence and wash-out of lime typically occurs on masonry units. During wetting, rain runs off the masonry surfaces and cause excessive wetting of the mortar joints. This facilitates dissolution of lime in the pore water of the mortar joints and prevents carbonation of this lime.

Most efflorescence can be washed away by high-pressure water. Acid solutions will also dissolve and remove the efflorescence from surfaces. Efflorescence can be limited or prevented through proper drainage and concrete sealers can also prevent efflorescence from reoccurring. The use of lime and GGBS in mortar mixtures would effectively eliminate efflorescence in masonry structures.

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