Masonry Magazine April 1971 Page. 31
Vanadium Stains
The chloride salts of vanadium require highly acidic leaching solutions, and are usually the result of washing brickwork with acid-cleaning solutions. Vanadyl chloride, one of the most prominent types of these stains, forms almost exclusively as a result of washing with hydrochloric acid. As stated by Brownell (Ref. 1): "A highly acid condition in the water leaching through a brick is necessary for the promotion of the colored vanadyl salts."
The prevention of green stain caused by vanadium is important, since subsequent to its appearance, efforts at cleaning may turn it into a brown insoluble deposit that is very difficult to remove.
To minimize the occurrence of green stain, the following steps are recommended:
* Store brick off the ground and under protective covers.
* Never use or permit the use of acid solutions to clean light colored brick.
* Seek and follow the recommendations of the brick manufacturer for cleaning procedures.
Green vanadium stains can be difficult to remove. Some methods and procedures for the removal of green stain are described in Technical Notes 20, "Cleaning Clay Products Masonry." Never attempt to remove green stain with acids.
Own Stain
Under certain special conditions, tan or brown and sometimes gray colored staining may occur on the mortar joints of brickwork. Occasionally, the brown stain will streak down onto the face of the brick. This is the result of the use of manganese dioxide as a coloring agent in the brick units. This type of staining problem is closely related to the general efflorescence problem, since it is the sulfate and chloride salts of manganese that travel to the surface of the brick and form on the mortar joint.
During the firing processes, the manganese coloring agents go through several chemical changes, resulting in none of the manganese compounds having solubility in water. But, they have varying degrees of solubility in weak acids. As previously discussed, acid solutions can prevail in the brick of a wall. Also, the brick can pick up hydrochloric acid by absorption during the cleaning process of the masonry. It is also possible that in some highly industrialized areas rain water may be acidic (Ref. 3).
According to Brownell (Ref. 1): "The manganese sulfate or chloride solutions from the brick will migrate across the mortar joints especially during a period of drying. These acidic manganese solutions will be neutralized by the inherent basic nature of the mortar. Upon neutralization, insoluble manganese hydroxide is precipitated on the mortar joints, and this is converted to brown Mn304 on drying."
To minimize or eliminate manganese stain, the following are suggested:
1. When a building is under construction with a manganese colored brick, it should not be cleaned with hydrochloric acid without neutralizing the acid during the rinsing operation. Such neutralization will tend to reduce the amount of manganese taken in the solution.
2. Application of silicones to brick (if otherwise unobjectionable, see Technical Notes 7, "Dampproofing and Waterproofing Masonry Walls") may prevent staining by retarding water penetration of the brick while stored or in service.
3. Always request and follow the advice of the brick manufacturer in cleaning a brown or manganese colored brick.
The removal of manganese stain is a fairly simple operation, and is described in Technical Notes 20, "Cleaning Clay Products Masonry." However, the permanence of the removal is often in doubt. Hence, the prevention of the occurrence of brown manganese stain is of paramount importance.
SUMMARY
This issue of Technical Notes has presented a brief description of the causes, mechanisms, and sources of efflorescence. Future issues of Technical Notes in this series will discuss the prevention of efflorescence, a guide for analysis of efflorescence problems, and the removal of efflorescence salts from the face of masonry.
REFERENCES
1. W. E. Brownell, "The Causes and Control of Efflorescence on Brickwork", Research Report, No. 15, SCPI, 1969.
2. J. E. Young, "Backup Materials as a Source of Efflorescence", Journal, American Ceramic Society, 40 (7), 1957.
3. F. O. Anderegg, "Efflorescence", ASTM Bulletin, No. 195, 1952.
4. T. Ritchie, "Study of Efflorescence Produced on Ceramic Wicks by Masonry Mortars", Journal, American Ceramic Society, 38 (10) 1955.
5. W. E. Brownell, J. L. Kenna, and P. P. Wilko, Jr., "Staining of Mortar by Manganese Colored Brick", Bulletin, American Ceramic Society, 45 (12), 1966.
6. T. J. Minnick. "Effect of Lime on Characteristics of Mortar in Masonry Construction", Bulletin, American Ceramic Society, 38 (5). 1959.
7. Technical Notes on Brick and Tile Construction, SCPI
* "Cold Weather Masonry Construction".
* "Dampproofing and Waterproofing Masonry Walls".
* "Cleaning Clay Products Masonry"