Foundation crack repair: Efflorescence occurs with all concrete and is the most common problem that concrete contractors face with colored concrete. Owners might not be worry about “plain” concrete, but colored concrete is another matter. They might quetch that their contractor didn’t give them the color they ordered, and sometimes they withhold payment. Efflorescence might be induced when soluble salts and other water dispersible materials come to the surface of concrete and mortars. 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 when it expose to moist or cool conditions or gradually, especially when it comes from within the concrete or from the sub-grade.
Material which are containing portland cement may results in efflorescence. The most usual reaction occurs when calcium hydroxide formed in the hydration reaction of portland cement is imparted by water to the surface through capillaries in the concrete. There it conflates with carbon dioxide which is coming from the air to produce calcium carbonate (an insoluble material) and water. But efflorescence can also be actuated by hydroxides and sulfates of either sodium or potassium, which are much more soluble in water than calcium. And they form efflorescence more quickly than calcium hydroxide. Sources of these salts are cement, aggregates, water, or admixtures.
Normally efflorescence is white and shows up 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 can be needed to cause a significant shift in color. Some forms are very tough to remove, while others are easy—especially if they are removed right after they form.
Efflorescence solution:
The easiest time to get rid of the calcium hydroxide efflorescence is before it combines with carbon dioxide. Up to this time it will dissolve in water, so either pressure washing or wet scrubbing will put it in solution with water so it can be rinsed away. You must be careful to rinse the surface with fresh water so that no residue is left to dry on the concrete. Use an air jet or a wet vacuum to remove any standing water. Any remaining solution will induce new efflorescence to appear.
When efflorescence goes forward to the calcium carbonate phase, it becomes insoluble and is much more difficult to remove—perhaps impossible. Usage of mild acid solution becomes the first course of action. These acids containing vinegar, muriatic acid, or citric acid. Concentrated Muriatic acid must be purchased and then it should be diluted. So it’s the most dangerous, requiring proper safety gear. After acid wash, slabs should be rinsed thoroughly and neutralized with baking soda. Acid residues can harm plants. The reaction products of acid on concrete are all soluble salts such as, calcium and iron salts, which can cause more efflorescence.
When efflorescence can’t be got rid of with acid washes, other commercial products are available. One is ethylenediamine tetraacetic acid (EDTA), this will quickly dissolves calcium salts. EDTA will also damage concrete, so it’s best to test it on an inconspicuous sample area first.
Efflorescence naturally occurs on all concrete. Part of the problem—and the solution—may have to do with the way we sell colored concrete. Customers often thought that their concrete will have uniform color. But they must be sold on the idea that concrete has variable color, providing interest and the impression of color depth.
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