Backup Materials as a Source of Efflorescence

Because white stains on the face of brick masonry walls are often the same salts that are associated with Portland cement, an investigation was made to determine whether efflorescing salts can originate in concrete backup block. The soluble‐salts content was determined for selected clap brick, concrete block, and clay tile; wick tests were run on the material. Composite walls were built of nonefflorescing brick backed with clay tile or with concrete block; high humidity was maintained on the back side of the walls and the moisture was allowed to migrate to the dry brick face. The discoloration of the face brick was compared and the salts were identified.