Efflorescence is not considered a stain but will be discussed here for identification purposes. Efflorescence is normally a harmless deposit of watersoluble, white salt crystals. In some instances efflorescence may appear on mortar joints.

Efflorescence may appear in limited areas on the surface of brickwork, and in extreme cases, cover the entire brickwork surface. Efflorescence is usually white in color; however, all white stains on brick masonry are not necessarily efflorescence. Lime run and white scum, as discussed below, are occasionally mistaken for efflorescence.

Silicate deposits, sometimes referred to as “white scum,” usually appear as white or gray discolorations on the face of brick masonry. Discoloration may be present over the entire face of the Lime Run brickwork or in smaller, irregularly shaped areas.

White scum may also occur adjacent to trim elements, precast concrete and, occasionally, large expanses of glass. A number of mechanisms may precipitate white scum on brickwork. White scum is typically related to the cleaning of brickwork with unbuffered hydrochloric (muriatic) acid solutions or inadequate prewetting or rinsing of the brickwork during cleaning.

Silicate deposits on brick masonry should not be confused with scumming that sometimes occurs on brick during the manufacturing process. This type of scumming will be evident on brick before they are placed in the wall.

Some brick develop yellow or green salt deposits when they come in contact with water or unbuffered hydrochloric (muriatic) acid. These stains are usually vanadium salts. They may be found on red, buff or white brick; however, they are more conspicuous on lighter-colored brick. The vanadium salts responsible for these stains originate in the raw

materials used for the manufacture of the brick.

The yellow and green stains are usually vanadyl salts, consisting of sulfates and chlorides, or hydrates of these salts. Vanadium stains occur in a manner similar to efflorescence, except that vanadium oxide and sulfates are dissolved and result in a solution that may be quite acidic. As water evaporates from this solution at the surface of the brickwork, vanadyl salts are deposited. The chloride salts of vanadium, such as vanadyl chloride, may form as a result of washing with unbuffered hydrochloric (muriatic) acid or excessive moisture exposure.

Preventing vanadium stains is important, since they can be difficult to remove and improper cleaning efforts may result in a brown, insoluble deposit. To minimize the potential for vanadium stains, the following steps are recommended:

- Store brick off the ground and under nonstaining protective covers.

- Never use or permit the use of highly-concentrated, unbuffered hydrochloric (muriatic) acid solutions to clean light-colored brick.

- Seek and follow the cleaning recommendations of the brick manufacturer.

Under certain conditions, tan, brown, or occasionally gray staining may occur on the mortar joints of brickwork. Occasionally, a brown stain will streak down onto the faces of the brick. This type of stain is the result of having a manganese oxide as a coloring agent in tan, brown, black or gray brick and its reaction to an acid.

During the brick firing process, the manganese coloring agents undergo several chemical changes, resulting in manganese compounds that are insoluble in water. They have varying degrees of solubility in weak acids. Once dissolved, these compounds may migrate in solution toward the surface of brickwork. As previously discussed, acid solutions can occur in brickwork under certain conditions.

Brick may also absorb unbuffered hydrochloric (muriatic) acid during cleaning. It is also possible that some geographical areas may be subject to acid rain. Manganese staining is closely related to efflorescence, since it is the sulfate and chloride salts of manganese that travel to the surface of the brickwork. When the solution reaches the mortar joints, the

salts are neutralized by the cement or lime in the mortar producing insoluble manganese hydroxide.

The manganese hydroxide precipitate is deposited on the mortar joint and when dry converts to brown manganese tetroxide resulting in the stain. Unbuffered hydrochloric (muriatic) acid should not be used to clean tan, brown, black or gray brick. Proprietary cleaning compounds are available for cleaning brick containing manganese. Test for effectiveness and follow the advice of the brick manufacturer.