Efflorescence is not a stain. Efflorescence is a powdery and sometimes ‘fluffy’ deposit that forms on the surfaces of porous building materials such as bricks, masonry units, mortar and concrete. The temporary appearance of efflorescence is common on new masonry especially brickwork.
In chemistry, efflorescence (which means “to flower out” in French) is the loss of water (or a solvent) of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.
Efflorescences can occur in natural and built environments. On porous construction materials it may present a cosmetic problem only, but can sometimes indicate serious structural weakness.
The formation of efflorescence requires 3 conditions:
• Presence of soluble salts.
• Excessive amounts of water entering the masonry (that is why it is very common after pressure cleaning new bricks).
• The evaporation of water as the masonry dries out, depositing salts on the surface.
Salts that appear as efflorescence can enter the wall from various sources:
• Mortar components, particularly cement.
• Soil or fill in contact with the wall.
• Sea spray in coastal areas.
• Masonry units, however this is not a common source.
Any situation that allows excessive amounts of water to enter the wall is likely to promote efflorescence.
The most common causes are:
• Poor coping and flashing.
• The failure to protect new brickwork when rain interrupts bricklaying.
• Poor storage of masonry units on site. Before units are placed in the wall they can absorb ground salts and excessive water in the stockpiled masonry and can mobilize latent salts if they are present in the masonry.
• Persistent efflorescence may be a warning that water is entering the wall through faulty copings, flashings or pipes.
• Efflorescence as seen on brick faces
• Efflorescence from ground salts
Primary efflorescence is named such, as it typically occurs during the initial cure of a cementitious product. It often occurs on masonry construction, particularly brick, as well as some fire stop mortars, when water moving through a wall or other structure, or water being driven out as a result of the heat of hydration as cement stone is being formed, brings salts to the surface that are not commonly bound as part of the cement stone. As the water evaporates, it leaves the salt behind, which forms a white, fluffy deposit, that can normally be brushed off. The resulting white deposits are referred to as “efflorescence” in this instance. In this context efflorescence is sometimes referred to as “saltpetering.” Since primary efflorescence brings out salts that are not ordinarily part of the cement stone, it is not a structural, but, rather, an aesthetic concern.
For controlling primary efflorescence, formulations containing liquid fatty acid mixtures (e.g., oleic acid and linoleic acid) have been commonly used. The oily liquid admixture is introduced into the batch mix at an early stage by coating onto the sand particles prior to the introduction of any mix water, so that the oily admixture is distributed uniformly throughout the concrete batch mix.
Secondary efflorescence is named such as it does not occur as a result of the forming of the cement stone or its accompanying hydration products. Rather, it is usually due to the external influence of concrete poisons, such as chlorides. A very common example of where secondary efflorescence occurs is steel-reinforced concrete bridges as well as parking garages. Saline solutions are formed due to the presence of road salt in the winter. This saline solution is absorbed into the concrete, where it can begin to dissolve cement stone, which is of primary structural importance. Virtual stalactites can be formed in some cases as a result of dissolved cement stone, hanging off cracks in concrete structures. Where this process has taken hold, the structural integrity of a concrete element is at risk. This is a common traffic infrastructure and building maintenance concern. Secondary efflorescence is akin to osteoporosis of the concrete.
For controlling secondary efflorescence, admixtures containing aqueous-based calcium stearate dispersion (CSD) are often added at a later stage of the batching process with the mix water. In a typical batching process, sand is first charged into the mixer, then the oil-based primary anti-efflorescence admixture is added with constant mixing to allow the oil to coat the sand. Then coarse aggregates, colorants, and cement are added, followed by water. If CSD is used, it is then introduced usually at this point during or after the addition of the mix water. CSD is an aqueous dispersion wherein fine solid particles of calcium stearate are suspended in the water uniformly. Commercially available CSD has an average particle size of about 1 to 10 micrometres. The uniform distribution of CSD in the mix may render the resulting CMU water repellent, as CSD particles are well distributed in the pores of the unit to interfere with the capillary movement of water.