Efflorescence
Efflorescence is the “frost” that sometimes appears on cementitious products.
Anything made with cement is susceptible to “frost” or efflorescence. Whether it’s concrete blocks and the mortar used to hold them in place, segmental retaining walls units, concrete roofing tiles or pavers, even poured concrete for roads, sidewalks, patios, or driveways, efflorescence may happen.
The good new is, we know how and why efflorescence occurs. The bad news is that efflorescence is almost impossible to prevent. The silver lining is that efflorescence eventually goes away, although it may take a year or two.
Efflorescence comes from within the concrete itself.
All concrete products contain cement, and cement inherently contains lime. To make a concrete product, in addition to cement, a manufacturer as specific amounts of other raw materials including sand, rock, water, chemical admixtures and pigments. These materials are mixed together then poured or molded into a specific shape. After all this happens, material sits or cures for a period of time.
Although the concrete product is solid and usable after curing, it contains, millions of microscopic pores or capillaries that go from the surface of the product down into it’s interior. As soon as the product starts to harden - which it will do for quite a while - the process of efflorescence may start.
How does Efflorescence occur?
Water necessary to make the concrete, rain, moisture from dew or even water from your sprinkler system, reacts with the free lime in the cement forming calcium hydroxide. As the concrete product dries out, the water migrates to the surface through the pores in the concrete product carrying with it the calcium hydroxide. When the calcium hydroxide comes in contact with carbon dioxide in the air, a hard white substance forms which sticks to the surface of the concrete after the moisture evaporates. This is the "frost" or efflorescence that you see. It will continue to form so long as the concrete is curing and the calcium hydroxide is free to move to the surface. The efflorescence phenomenon will stop when no more calcium hydroxide forms.
Technically, efflorescence is a calcium carbonate precipitate:
CaO + H2O ---> Ca(OH),
Ca(OH2) + CO2 -> CaCO, H2O
Just be patient. Efflorescence will go away.
The hard white "frost" eventually will dissolve in the presence of rainwater and carbon dioxide, and wash away, but it takes time. Consequently, if you live in an area of frequent rain followed by sunny days, the entire process of efflorescence -- from formation to elimination -- will happen quickly. On the other hand, if you live in a dryer more arid climate the entire process will obviously take longer.
Technically speaking, the "frost" degrades to water soluble calcium bicarbonate:
CaCO,+ 2CO, + H2O --> Ca(HCO),
What if I can't wait?
If the "frost" is so obvious and detracts from the beauty of your concrete product, a very diluted acid solution can remove efflorescence. You must know, however, that the acid can change the surface of your product, and that will alter its appearance. This change becomes especially noticeable on products that are colored with iron oxide pigments.
If you feel you must do something about efflorescence, you can follow these steps.
Method 1:
• Try Cathedral Stone Products’ Efflorescence Remover.
Method 2:
1. Put on protective goggles and gloves for mixing and application. A long sleeve shirt should also be worn.
2. Wet surface thoroughly with water
3. Mix water with hydrochloric (muriatic) acid. To dilute the acid, add 1 part acid to 10-20 parts water, making certain to add the acid to the water carefully.
4. Use a stiff brush to apply the diluted acid.
5. Allow the solution to stay on the surface for about 15 seconds.
6. Wash it off thoroughly with water.
Make certain to follow (1) the concrete product manufacturers recommendations and use appropriate safety precautions, and (2) all applicable environmental regulations managing wastewater resulting from the procedure.
Bayer makes Bayferrox iron oxide pigments, and it's these pigments that bring concrete products to life. From deep plum to terra cotta shades of red, soft yellow through intense blacks, or virtually any shade of brown imaginable, it's the Bayferrox pigments that turn dull gray concrete into a work of art.
Bayferrox pigments do not cause efflorescence nor can they prevent it from happening. Efflorescence, unfortunately, is just more visible on colored products due to the lighter color of the "frost." Bayferrox pigments are lightfast and weather stable, and meet or exceed all requirements set forth by the American Society for the Testing of Materials (ASTM) for pigments used to integrally color concrete products.Therefore, the concrete products retain their strong colors for decades, even under extreme weather conditions. Long after the efflorescence has gone away, the rich Bayferrox colors will remain.