Efflorescence
Information About Salt Deposits
Efflorescence is a crystalline sedimentation on surfaces of masonry, roof tile or concrete. It’s whitish in appearance, and is occasionally referred to as “whiskers”. Masonry Efflorescence has represented a problem for a lot of years, and is a subject of much contention. The geological formation of these salt deposits are not secrets. They are, largely, water-soluble salts that are derived from several potential origins to blemish and detract from an otherwise aesthetic and durable structure. First off, there must be water present to dissolve and carry the salts. Groundwater is frequently a source of efflorescence. For water to transport or move the salts to the surface there must be channels through which to move and transmigrate. The denser the material, be it brick, stone, roof tile or concrete, the harder for the water to carry salts to the surface. Conversely, the more permeable the material, the greater the ease with which salts are transferred and deposited. Salt carrying water, upon arriving at the surface of a structure, air evaporates to deposit the salt. When humidity is down, the water could evaporate prior to reaching the surface of the structure, leaving the salt deposit underneath the surface, and undetected. When the humidity is high, water evaporation is more gradual allowing for more opportunity for efflorescence growth. Maturations which project 1/4 to 1/2 inch beneath the surface have been described in a few regions of the country.
The mechanisms by which efflorescing salts are transported to the surface of structures by moisture and capillary tubing action via porous materials, is comprehended. The quantity and character of the material deposited changes considerably, contingent upon the nature and origin of the soluble materials.
Constitution of Efflorescence
The trouble of efflorescence, or the deposit of water-soluble salts on the surfaces of masonry, roof tile or concrete, is an age old one, and one that’s been analyzed and reported about as early as 1877. These accounts are all in basic agreement that efflorescence arises from more than one origin, and perhaps made up of more than one or two compounds.
Additionally, other salts such as chlorides and nitrates, and salts of vanadium, chromium and molybdenum are noted without providing specified composition. These last, in particular vanadium, are stated to create green efflorescence on white or buff burned clay units, although other salts produce white or gray sediments. Efflorescence descended from complex vanadium compounds contained in the clay utilized in brick fabrication isn’t unusual in the southwest part of the United States.
Sources of Efflorescence
There is many sources for water-soluble salts with many salts more dissolvable than others. The apparent movement of groundwater into building foundations and by capillary vessel action, or wicking, upward into masonry, stucco or concrete, is very often the cause of Masonry Efflorescence. In the case wherever soil conditions display water soluble sulfates, cautions should be aimed to prevent the passing of this sulfate-bearing water to the structure. Low absorption is the better sureness against efflorescence. Properly graded aggregates, low water-cement ratio, good compaction and appropriate curing practices will create concrete of maximal density and low water absorption.
Sand and crushed rock, in their natural state, may or may not have been connected with salt bearing water or soil. Whenever they have, and these salts are not extracted by washing away, this can be a potential source for Masonry Efflorescence. Most stone, sand and gravel plants, nevertheless, are careful in washing material so that any contribution made to efflorescence from this source is minimal.
When mixing-water utilized for mortar, roof tile or concrete is obtained from a natural origin which has been in contact with a sulfate-bearing soil, the ensuant structure might display efflorescence. The adhesion, again, to a good concreting practice of low water-cement ratio, will help reduce the appearing of salts of this source.
A different potential source of soluble salts are clay products, such as construction brick and face brick. Typically, in the present day fabrication of these products, the highly soluble salts are washed from the clay, and a barium salt such as barium carbonate is added to the product, to respond with the calcium sulfate which may be present. In this chemical reaction, the product is two reasonably insoluble compounds-barium sulfate and calcium carbonate. When produced in this way, clay products demonstrate little propensity to efflorescence.
Construction brick must be stored in a dry place off the ground to forbid soaking up of moisture or dampness from potential salt bearing soil. An acceptable test may be made to show the capability of brick to add to Masonry Efflorescence through soluble salt content. A brick is placed on end in a pan of distilled water for 7 days, in which time water is absorbed upwards and through the brick and then evaporated from the surface. Soluble salts are taken into solution by the water and deposited on the surface.
It’s likewise been noticed that the occurrence of Masonry Efflorescence bears a relationship to the type of mortar utilized. With a specific type of brick and a certain mortar no efflorescence may occur, whereas, the same brick with a different mortar could produce a wall heavily glazed with salt deposits. The appearance of sodium and potassium salts (as sulfates) generally suggest portland cement mortar as the source. The use of low alkali cement in mortar and grout will minimize efflorescence, at least from this generator.
Since, largely, concrete masonry is reasonably porous, evaporation of the salt bearing water typically takes place prior to reaching the surface when exposed to a drying atmosphere. The hydroxides are converted by reaction with thecarbon dioxide of the air to alkali and calcium carbonates. Efflorescence in the form of alkali chlorides and sulfates is formed when the structure is surrounded, exposed, or in touch with salt-bearing water or soil and comes out as columnar or whisker-like crystallizations.
Many of the sources of water-soluble salts have been addressed. These may be deposited on roof tile, masonry or concrete walls as efflorescence. Practically any construction materials in direct contact with the ground are potential sources for water-soluble salts. This information has been acknowledged by the several producers of construction materials, and steps have been assumed to reduce their presence to a great degree.
Removing of Efflorescence
Assorted processes have been utilized in attempts to remove Masonry Efflorescence from masonry constructions. It’s been discovered that when efflorescence is induced by soluble alkali salts, the salts will dissolve in water applied to the structure and transmigrate back into it. These salts would then re-emerge on the surface as the structure redried. It was determined consequently, that the best way to remove these soluble salts was to brush the surface thoroughly with a stiff brush. Water, however, has been acceptable for removing efflorescence from the face of concrete structures, since concrete is reasonably well saturated with water. In fact, efflorescence in the form of alkali salts will be washed from the surface of concrete structures, if exposed to rain, over some time period. If the coating is largely calcium carbonate or calcium sulfate, it bonds rather strongly and is difficult to remove by brushing. The practice developed in this case for masonry surfaces, has been to saturate the structure as thoroughly as conceivable with water, and then wash with diluted muriatic acid, followed instantly with an alkaline wash, then washed with water.
A great deal care must be taken in applying acid to portland cement products. The acid will attack, not only the calcium carbonate and calcium sulfate efflorescence, but also other calcium compounds to produce calcium salts such as calcium chloride. It is, consequently, very important to neutralize the acid before it can attack other compounds.