Efflorescence is a harmless salt-based residue that occurs on surfaces such as concrete, brick, and masonry. It can be removed with water or chemicals like muriatic acid. Prevention methods include adding silicone sealants to mixes to prevent water from evaporating and leaving residue.
Efflorescence is the residue that remains after the water has been removed. The residue is mostly salt-based and harmless. Several types occur in the construction industry, including concrete, brick and masonry. An efflorescence remover is typically available to prevent unsightly buildup on surfaces.
In concrete, efflorescence occurs when the water used to mix the original cement powder begins to dissolve the salt that occurs naturally in the mix. As the water evaporates over time, the salt is drawn to the concrete surface and leaves a residue. Most cement is gray or white, so the residue is usually not that obvious.
Efflorescence on bricks, on the other hand, is usually more evident because the white powdery residue can stand out against the reddish color of some bricks. The water used to mix the mortar that is used between the bricks is often where the residue originates. Mortar efflorescence can usually be removed using a stiff brush with water. If the residue is more pronounced over a larger amount of space, another option may be pressure washing.
The efflorescence of the masonry is also caused by the evaporation of water leaving deposits of crystallized salt. New construction may not reflect the problem, but a bloom of new construction may occur after several weeks as water works its way to the surface. Wet conditions such as continuous rain or hairline cracks in the masonry can often make the event more serious.
Cleaning for severe conditions that don’t resolve with hand washing or pressure washing may require chemicals. The most common chemical used to treat the problem is muriatic acid. This treatment usually washes away the efflorescence, but also removes a thin layer of the surface; it is typically only used under extreme conditions. The acid is diluted in water then spread over the affected surface. As soon as the residue is eaten, it is sprinkled with baking soda or ammonia on the surface to neutralize the acid and prevent erosion.
While total prevention is not possible, steps are often taken to reduce the likelihood and severity of efflorescence. The most common method is to add silicone sealants to concrete and masonry mixes to seal the surface. This is achieved when the silicon reacts with the lime in the mix which results in calcium silicate. The calcium silicate acts as a barrier and prevents water from evaporating to the surface which in turn prevents salt residue from being left behind.
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