Masonry Magazine June 1982 Page. 17
Sand
Sand. The sands used in construction and in mortar are primarily silica, and as such they are not water soluble. Sands, however, may be contaminated with material which will contribute to efflorescence. This contamination may include: sea water, soil runoff, plant life and decomposed organic compounds among others. Any of these may contribute to efflorescence.
Miscellaneous Sources of Salts
In addition to the mortar and units placed in the construction assembly, there are other outside sources of 'efflorescing soluble salts that may contribute to efflorescence. Some of these are discussed here.
Admixtures. A wide variety of admixtures for masonry mortars is available on the market. Most of these products are proprietary and their compositions are not disclosed. In general, they classify as grinding aids and air-entraining agents, water repellents or wetting and air-entraining agents, and accelerators.
Available data on the effect of these admixtures on the properties of mortar are limited to their effect on flow, water retentivity and strength. Little information has been published as to their effect on bond, either between mortar and brick or between mortar and reinforcement. In addition, there is some evidence, based largely on field experience, that certain admixtures have a detrimental effect upon bond between mortar and brick. This reduction in bond will make masonry walls more vulnerable to water penetration.
For these reasons, unidentified admixtures are not recommended for use in mortars unless it has been established by experience or laboratory tests that they will not materially impair mortar bond, and that their ingredients will not contribute to efflorescence.
Calcium Chloride. Calcium chloride is sometimes added to mortar as an accelerator as provided for in ASTM Specifications C 270, "Mortar for Unit Masonry." Its use should not be permitted in masonry containing metal anchors or reinforcement, as there is evidence linking the corrosion of metal embedded in mortar with the use of calcium chloride.
If, however, calcium chloride is used, it should be limited to an amount not to exceed two per cent by weight of the portland cement or one per cent of the masonry cement (usually about 50 per cent portland cement) content of the mortar (see Technical Notes 1A). Normally, this amount of calcium chloride will not contribute materially to efflorescence, however, larger amounts may do so.
Ground Water
Ground Water. Soluble salts in the soil are dissolved by water which penetrates the ground. Consequently, most ground water contains a high concentration of these salts. When the earth is in contact with the masonry, ground water may be absorbed by the masonry and, through capillary action, may rise several feet above the ground within the assembly, thus producing an accumulation of salts in the masonry.
Atmosphere
Atmosphere. It has been reported by some investigators (Ref. 3) that sulfurous gases in the atmosphere, especially in and around certain industrial installations, may contaminate the brickwork with soluble salts through soaking by acidic rain. This situation over a period of time could possibly cause some disintegration of the mortar and perhaps attack the components of the brick itself. The reporting of such instances, however, are infrequent and then limited to highly industrial areas and coastal regions.
Sources of Moisture
As previously discussed, the mechanism of efflorescence is dependent upon the presence of free water in the construction assembly to take any available soluble salts into solution. Some of the sources of free water are discussed in the following paragraphs.
Rain Water
The primary source of moisture for the occurrence of efflorescence is rain water which penetrates or comes in contact with the masonry assembly containing soluble salts. The exposures of the masonry assembly to rain water vary greatly throughout the United States from very severe on the Atlantic Seaboard and Gulf Coast where rains of several hours duration may be accompanied by high winds, to moderate in the Midwest and Mississippi Valley where wind velocities are lower, to slight in arid areas of the West. Exposure area may be defined roughly in terms of wind pressure and annual precipitation. The maps of Fig. 2 indicate geographic areas of high wind pressures and heavy precipitation.
Rain water may penetrate masonry walls which are improperly designed or improperly detailed. The craftsmanship employed in the construction of a masonry wall may also have a material effect on the degree or the amount of water penetrating the wall. Workmanship characterized by partially filled joints, deep furrowing of the mortar beds, and improper execution of flashing and caulking details will be more subject to rain penetration. This subject will be discussed further in other Technical Notes in this series.
FIG. 2
terized by partially filled joints, deep furrowing of the mortar beds, and improper execution of flashing and caulking details will be more subject to rain penetration. This subject will be discussed further in other Technical Notes in this series.
Condensation
In addition to rain water and ground water which may penetrate masonry walls, water may accumulate within the wall as a result of condensation of water vapor. Frequently, efflorescence that appears on rain-resistant masonry walls is due to this accumulation of water.
Condensation is usually due to moisture originating inside buildings. The moisture content of the outside air, which enters the building and is heated for comfort purposes, is invariably increased by moisture released from cooking, bathing, washing and other operations employing water or steam, and by the moisture released by exhalation and perspiration from the occupants. This gain in moisture content of the air increases the vapor pressure substantially above that existing in the outdoor atmosphere. This increased pressure tends to drive the vapor outwardly from the building through any vapor-porous materials that may comprise the enclosing surfaces.
When vapor passes through porous and homogeneous materials, which may be warm on one side and cold on the other, it may pass through the zone of its dew point temperature without condensing into water. But, if the flow of vapor is impeded by vapor-resistant surfaces at a temperature below the dew point temperatures, the vapor may condense upon such cold surfaces. This condensed moisture can contribute to efflorescence on the surface of the wall.
Construction
Another source of water which may cause "new-building bloom" and contribute to future occurrences of efflorescence in a building is the water which enters the assembly during construction. The improper protection of a building during construction phases may materially contribute to future problems, including efflorescence. It is at this stage, when interior assemblies are exposed, joints are open and foreign materials are present on the project, that the construction is highly vulnerable to the entry of considerable moisture. Also, in some cases, additional soluble salts from other sources may contaminate the wall assembly.
OTHER EFFLORESCENCE STAINS
There will occasionally occur on the surfaces of masonry structures stains other than the fairly common white efflorescence previously discussed. These are "green stains" and "brown stains."
Green Stain
Some structural clay products develop yellow and green efflorescence salts when they come in contact with water. These stains are usually vanadium salts. They can be found on red, buff or white clay products; however, they are most objectionable and usually noticed on the lighter color units. The vanadium salts responsible for these stains have their origin in the raw material used for the manufacture of clay products. The yellow and green stains which appear as efflorescence on brick are usually vanadyl salts consisting of sulfates and chlorides, or hydrates of these salts.
The mechanisms of this type of efflorescence are as follows: as water travels through the brick it dissolves both the vanadium oxide and sulfates. In this process the solution may become quite acidic. As the solution evaporates from the surface of the product, the salts are deposited.