What Is Efflorescence?

Definition & Examples of Efflorescence

Stone mason carving stone with mallet and chisel

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Efflorescence is a crystalline or powdery deposit of salts often visible on the surface of concrete, brick, stucco, or natural stone surfaces. It occurs when water leaves behind salt deposits on the masonry surface.

The word efflorescence means "to flower out" in French, but this flowering leaves an unattractive residue behind. It sparkles; it's white, sometimes with a grayish tint; and flakes off the masonry surface. Learn what causes this unsightly occurrence and how to prevent or remove it.

What Is Efflorescence?

You can easily recognize efflorescence on walls, floors, retaining walls, and other surfaces made of brick, stone, concrete, or stucco. It's often a white, powdery substance when seen on unsealed surfaces.

If a floor or other concrete surface has been sealed, you may see efflorescence as a white blush under the sealer. This can be especially concerning for homeowners who have sealed concrete floors.

If you're a homebuyer, a real estate home inspection would reveal whether your soon-to-be home has efflorescence. Some astute real estate agents might note efflorescence in the home, most likely to be prevalent on basement walls. Wet basements, especially, are the perfect environment in which efflorescence can grow.

Efflorescence is composed of a variety of water-soluble salts. Different surfaces and different areas of the country are more likely to have particular combinations, which lead to a variety of colors.

How Does Efflorescence Happen?

For efflorescence to occur, you need water and salt. The salt comes from a range of sources. First, it may already be present inside the brick, stone, or concrete. Or the source may be the grout or cement holding surfaces together. If the surface, such as a retaining wall, is in contact with soil, efflorescence could form. Finally, in areas with hard water, it could be present in the water itself.

The salt must be dissolved in water and transported to the surface of the masonry, stone, or concrete. The water may already be present in the surface itself. It could also come in from outside of the surface and dissolve the salts. Once this occurs, if the water can find a path to the surface and evaporate, it will leave behind crystallized deposits.

How Can You Control or Remove Efflorescence?

There are several construction techniques that can minimize the growth of efflorescence, such as controlling the amount of water used in mortar and grout, designing with eaves and copings to direct water away from surfaces, and paying attention to landscaping and irrigation. Sound construction practices will prevent water from wicking from the ground into masonry structures.

The best way to remove efflorescence depends on the surface and the composition of the salts. One method is to use a dry brush. For some salts, you can simply wash them away with a hand brush, mild detergent, and a water rinse. Power washing is another option, depending on the surface. You may want to consult with a contractor to see if there is a recommended chemical cleaning agent for your surface and get instructions on how to use it safely. For example, a weak solution of muriatic acid might be safe for some surfaces, but it could damage others.

In general, cleaning efflorescence from a surface is an ongoing solution—much like a treatment—rather than a cure. Sealing a surface might be a solution, but if water still finds its way into the surface, you could end up with cracking or spalling, which is a destructive process that should be avoided. Likewise, if you power wash or sandblast a surface incorrectly, you could increase the porousness of the masonry, letting more moisture in and compromising its integrity. Be sure you consult a professional about how to treat your efflorescence problem.

Key Takeaways

  • Efflorescence is a powdery or crystalline deposit—usually white, gray, brown, or yellow—on or underneath the surface of various types of masonry.
  • It is the result of water dissolving certain salts, migrating to the surface of the masonry, and evaporating to leave behind salty deposits.
  • Although unsightly, it is usually not a threat to the masonry unless treated improperly.
  • Efflorescence can often be prevented with the right construction methods or treated when it becomes visible.