Efflorescence is a natural occurrence caused when soluble salts and other water dispersible materials come to the surface of natural products. It's induced by low temperatures, moist conditions, condensation, rain, dew, and water added to the surface of fresh concrete to assist troweling. It can occur very soon after exposure to moist or cool conditions or gradually, especially when it comes from within the surface or from the subgrade. This is a clue that moisture is penetrating the surface and an improper draining issues exists.
Any material containing portland cement results in efflorescence. The most usual reaction occurs when calcium hydroxide (lime) formed in the hydration reaction of portland cement (approximately 140 pounds per cubic yard of concrete) is transported by water to the surface through capillaries in the concrete. There it combines with carbon dioxide from the air to produce calcium carbonate (an insoluble material) and water. But efflorescence can also be caused by hydroxides and sulfates of either sodium or potassium, which are much more soluble in water than calcium. And they form efflorescence more rapidly than calcium hydroxide. These salts can come from cement, aggregates, water, or admixtures.
Efflorescence is normally white but can vary in color and can be more noticable more on darker colors than white or light gray because of the contrast. Only 0.2 ounce of calcium carbonate per square yard of surface is needed to cause a significant shift in color. Some forms are very difficult (if not impossible) to remove, while others are easy—especially if they are removed right after they form.
Without treatment, Efflorescence can build up and damage the minerals in the surface creating voids and unappealling finishes. Surface Buff technicians can carefully remove and treat efflorescence. We cannot guarantee it will not return, however it typically reduces with each treatment.