Efflorescence: Some Causes and Prevention

"IntroductionEFFLORESCENCE is herein considered to be any deposit of salts on the surface of a masonry structure that is brought from within or through the structure by capillarity and deposited by evaporation. Usually, efflorescence is white although green, yellow, and brown efflorescence is sometimes observed.The common white efflorescence almost always consists of sulphates of the alkali and alkaline earth metals and calcium carbonate, although sodium chloride is frequently present in structures erected near the sea shore.The first and most obvious result of the presence of soluble salts in masonry is the unsightly accumulation of these salts on the surface. This is particularly noticeable early in its life and is frequently fugitive ( 1), as much of the salt is soluble and is gradually washed away by rain. This removal can usually be facilitated by scrubbing; the structure with dilute hydrochloric acid.A more serious effect is the continuous accumulation of soluble salts as a result of ingress of sulphur acids in rain water or water from the ground. This may eventually cause spalling and disintegration by crystallization of salts in the pores of brick and mortar. An example of this type of failure, resulting from the crystallization of calcium sulphate, is discussed by Hardesty (2). Butterworth (3) describes similar failure resulting from •crystallization of magnesium sulphate."