Efflorescence is a white, powdery deposit that appears on the surface of concrete, masonry, and stucco products. Its a very common occurence and, although its usually harmless, these deposits can be a real eyesore.
It goes unnoticeable on plain, gray concrete and block but becomes very visible on colored concrete and brick. Normally, the problem doesnt show up until weeks or months after installation and often becomes a dispute between angry customers and contractors.
Efflorescence is caused by water moving through concrete and masonry products. As it travels through in a process called capillary action, the water dissolves salts contained in the material. When the water reaches the outside, it evaporates and leaves the salts on the surface. Overtime the buildup of the salty deposits can become quite significant. This process is facilitated by lower temperatures, humidity, rain, or anything that will keep the material wet such as sprinklers.
There are two types of efflorescence. There's the regular or powdery kind that is easily removed. There's also crystallized efflorescence. This occurs when powdery deposits go through cycles of being redissolved, drying out, then redissolved again and so on. This forms crystals which begin to adhere tightly to the surface and require special cleaners or acids for removal.
Because humidity and moisture play a key role, some areas of the country will experience the problem more than others. The time of year also plays a part since some seasons are wetter than others.
Despite efforts of manufacturers and contractors to limit efflorescence in their products, they are using raw earth materials that contain salt and will vary in salt content from batch to batch and from one location to another.