Masonry Magazine June 1982 Page. 15
BIA Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road. McLean. Virginia 22102
INTRODUCTION
EFFLORESCENCE, CAUSES
Efflorescence, as used in this discussion, is a deposit of water-soluble salts upon the surface or in the pores of masonry. This deposit is usually white in color; although certain vanadium and molybdenum compounds, present in some ceramic units, produce a green deposit usually referred to as "green stain." Also, there is occasionally an instance of "brown stain" resulting from deposits of manganese compounds.
The principal objections to efflorescence are usually based on the appearance characteristics. However, while surface efflorescence is unsightly and a nuisance to remove, it is by no means as harmful as the efflorescent crystal pressure resulting from deposits within the pores of the masonry.
As stated by W. E. Brownell (Ref. 1):
"Under certain conditions, salts can be deposited below the surface of brick in the pores. When this takes place, the force of crystallization and growth of crystals can cause cracking and disintegration of the products."
It is the purpose of this issue of Technical Notes to present to the design professional; architect, engineer or specification writer, a basic understanding of the phenomena of efflorescence. Future issues of Technical Notes will present recommendations on how to prevent its occurrence, and a guide for its investigation, identification, and elimination.
MECHANISMS OF EFFLORESCENCE
The mechanisms of efflorescence are many and often complicated; however, simply stated, water-soluble salts are brought to the surface of masonry in solutions of water and deposited there by evaporation. The salts solution may migrate across the surfaces of the units or through the pore structure of the masonry.
There are certain simultaneous conditions which must exist for the phenomenon of efflorescence to occur. Soluble salts must be present within or in contact with the masonry assembly. These salts may be present in the facing units, backup, mortar ingredients, trim, etc. There must be a source of water and it must be in contact with the salts for sufficient time to take them into solution. The construction assembly must be such that pathways exist for the migration of the salts solution to the surface of the masonry, or other locations, where the salts are deposited by evaporation of the water.
It is apparent, from the above, that if masonry could be constructed containing no water soluble salts, or if no water penetrated the masonry, efflorescence would not occur. However, in conventional masonry exposed to weather, neither of these conditions can be met completely. Consequently, the practical approach to the elimination of efflorescence is to reduce all contributing factors to a minimum.
Sources of Salts
The chemical composition of efflorescence salts is usually alkali and alkaline earth sulfates, and carbonates; although, chlorides have also been identified on rare occasions. The most common salts found in efflorescence are sulfate and carbonate compounds of sodium, potassium, calcium, magnesium and aluminum. In rare instances, chlorides may occur as efflorescence, but this is usually a result of contamination of masonry units or mortar sand by sea water or the runoff from alkaline soils.
The problem of efflorescence is further complicated by the many available sources of soluble salts. Soluble salts may be present in the masonry units, in the mortar, or may result from the penetration of the masonry by rain water or ground water, or other sources as discussed hereafter.
Masonry Units
Since efflorescence, when it occurs, appears on the face of the wall, it is often erroneously assumed to be the brick that are at fault. This is not usually the case. There are, however,
Originally published in December 1969, this Technical Notes has been reviewed and reissued.