Efflorescence is a deposit of substances leached from the masonry either onto the surface or into the pores of brick masonry walls. These deposits may be the substances themselves or secondary reaction products of them with the atmosphere. Investigations of efflorescence on brick masonry walls on dozens of structures throughout the United States by the authors and their colleagues have revealed that the efflorescence on approximately 50 percent of the 43 samples studied consists of water soluble sulfate compounds and that the efflorescence on approximately 40 percent of the samples studied consist of calcium carbonate (carbonated calcium hydroxide) that is not soluble in water. Whenever sulfate compounds are predominant in efflorescence on brick masonry, the source of the efflorescence is usually the brick. Calcium carbonate “efflorescence” originates from the mortar. These data strongly suggest that water soluble efflorescence on brick masonry is most likely a sulfate compound which originated from the brick.
To reduce the potential for efflorescence development in brick masonry walls, the bricks manufactured for a specific building should be tested in accordance with ASTM C 67, Method of Sampling and Testing Brick and Structural Clay Tile. In addition, they should be chemically analyzed for water-soluble constituents to assess the efflorescence potential of the brick.
The potential for efflorescence development in brick masonry walls can also be reduced through the use of drainage type walls with a proper flashing and weep system and through the use of good construction practices and proper material selection.